title: Texarkana Moonlight Murders

text: Investigations were conducted at the city, county, state and federal level. In the course of investigations, there have been shifting opinions by officials over whether the first and fourth attacks were committed by the same perpetrator. The prime suspect in the case was Youell Swinney, a career petty criminal who was linked to the murders primarily by statements from his wife plus additional circumstantial evidence. After Swinney's wife refused to testify against him, prosecutors decided against pursuing murder charges. Swinney was convicted on other charges and sentenced to a long term as a habitual car thief and forger. Two of the lead investigators believed him to be guilty of the murders. The book "The Phantom Killer: Unlocking the Mystery of the Texarkana Serial Murders" (2014) concludes that Swinney is the culprit. The events inspired many works, including the 1976 film "The Town That Dreaded Sundown". This film is the basis for much of the subsequent myth and folklore around the murders.


title: Texarkana Moonlight Murders

text: The Texarkana Moonlight Murders involve four violent attacks which occurred over ten weeks from February to May 1946 in and around Texarkana, twin cities at the border of Miller County, Arkansas, and Bowie County, Texas, United States. All four attacks targeted male-female pairs in isolated locations, on weekend nights. The attacks took place at intervals of three to four weeks. Investigators speculated that the attacks were the work of an unidentified serial killer.


title: Texarkana Moonlight Murders

text: At around 11:45 p.m. on Friday, February 22, 1946, Jimmy Hollis, age 25, and his girlfriend, Mary Jeanne Larey, age 19, parked on a secluded road known as a lovers' lane after having seen a movie together. The area was approximately from the last row of city homes. Around ten minutes later, a man wearing a white cloth maskwhich resembled a pillowcase with eye holes cut outappeared at Hollis's driver-side door, and shone a flashlight in the window. Hollis told him he had the wrong person, to which the man responded: "I don't want to kill you, fellow, so do what I say."


title: Texarkana Moonlight Murders

text: Both Hollis and Larey were ordered out the driver-side door, and the man ordered Hollis to "take off [his] goddamn britches." After he complied, the man struck him in the head twice with a pistol. Larey later told investigators that the noise was so loud she had initially thought Hollis had been shot, but it was his skull fracturing. Thinking the assailant wanted to rob them, Larey showed him Hollis's wallet to prove he had no money, after which she was struck with a blunt object. The assailant ordered her to stand, and when she did, told her to run. Initially, she tried to flee toward a ditch, but the assailant ordered her to run up the road.


title: Texarkana Moonlight Murders

text: Larey spotted an old car parked off the road but found it empty, and was again confronted by the attacker, who asked her why she was running. When she said that he had told her to do so, he called her a liar before knocking her down and sexually assaulting her with the barrel of his gun. After the assault, Larey fled on foot, running a half-mile (800 m) to a nearby house; she woke the residents of the house and phoned the police.


title: Texarkana Moonlight Murders

text: Meanwhile, Hollis had regained consciousness and alerted a passing motorist who also called the police. Within thirty minutes, Bowie County Sheriff W. H. "Bill" Presley and three other officers arrived at the scene of the attack, but the assailant had already left. Larey was hospitalized overnight for a minor head wound. Hollis was hospitalized for several days to recover from multiple skull fractures.


title: Texarkana Moonlight Murders

text: Hollis and Larey gave conflicting reports of their attacker: Larey claimed that she could see under the mask that he was a light-skinned African American. Hollis alternately claimed it was a tanned white man, and around 30 years old, but conceded he could not distinguish his features as he had been blinded by a flashlight. Both agreed that the assailant was around tall. Law enforcement repeatedly challenged Larey's account, and believed that she and Hollis knew the identity of their attacker and were covering for him.


title: Texarkana Moonlight Murders

text: Richard L. Griffin, age 29, and his girlfriend of six weeks, Polly Ann Moore, age 17, were found dead in Griffin's car on the morning of Sunday, March 24, 1946, by a passing motorist. The motorist saw the parked car on a lovers' lane 100 yards (91 m) south of US Highway 67 West in Texas. The motorist at first thought that both were asleep. Griffin was found between the front seats on his knees with his head resting on his crossed hands and his pockets turned inside out; Moore was found sprawled face-down in the back seat. There is evidence that suggests she was placed there after being killed on a blanket outside the car.


title: Texarkana Moonlight Murders

text: Griffin had been shot twice while in the car; both had been shot once in the back of the head, and both were fully clothed. A blood-soaked patch of earth near the car suggested to police that they had been killed outside the car and placed back inside. Congealed blood was found covering the running board, and it had flowed through the bottom of the car door. A .32 cartridge casing was also found, possibly ejected from a pistol wrapped in a blanket.


title: Texarkana Moonlight Murders

text: No extant reports indicate that either Griffin or Moore was examined by a pathologist. Contemporaneous local rumor said that Moore had been sexually assaulted, but modern reports refute this claim.


title: Texarkana Moonlight Murders

text: At around 1:30 a.m. on Sunday, April 14, Paul Martin, age 17, picked up Betty Jo Booker, age 15, from a musical performance at the VFW Club at West Fourth and Oak Street. Martin's body was found at around 6:30 a.m. later that morning, lying on its left side by the northern edge of North Park Road. Blood was found on the other side of the road by a fence. He had been shot four times: through the nose, through the ribs from behind, in the right hand, and through the back of the neck.


title: Texarkana Moonlight Murders

text: Booker's body was found by a search party at about 11:30 a.m., almost from Martin's body. Her body was behind a tree and lying on its back, fully clothed. It was posed with the right hand in the pocket of the buttoned overcoat. Booker had been shot twice, once through the chest and once in the face. The weapon used was the same as in the first double-murder, a .32 automatic Colt pistol.


title: Texarkana Moonlight Murders

text: Martin's car was found about from Booker's body and away from his body. It was parked outside Spring Lake Park with the keys still in it. The authorities were not sure who was shot first. Sheriff Presley and Texas Ranger Captain Manuel Gonzaullas said that examinations of the bodies indicated that they both had put up a terrific struggle. Martin's friend, Tom Albritton, said that he did not believe an argument had happened between the victims and that Martin had not had any enemies.


title: Texarkana Moonlight Murders

text: On Friday, May 3, sometime before 9 p.m., Virgil Starks, age 37, and his wife Katie, age 36, were in their home on a farm off Highway 67 East, almost northeast of Texarkana. He was sitting in an armchair reading the newspaper when he was shot twice in the back of the head from a closed double window. Hearing the sound of broken glass, Katie came from another room and saw Virgil stand up then slump back into his chair. When she realized he was dead, she ran to the wall-crank telephone to call the police. She rang twice before being shot twice in the face from the same window. She fell but soon regained her footing and tried to get a pistol from another room, but was blinded by her own blood. She heard the killer at the back of the house and fled out the front door. She ran barefoot across the street to her sister and brother-in-law's house. Because no one was home, she ran to a neighbor A. V. Prater's house, gasped that "Virgil's dead", then collapsed.


title: Texarkana Moonlight Murders

text: Prater shot a rifle in the air to summon another neighbor, Elmer Taylor, who Prater sent to collect his car. Taylor complied and, along with the Prater family, took Katie Starks to Michael Meagher Hospital (now Miller County Health Unit). Starks was questioned in the operating room by Miller County Sheriff W. E. Davis, who became head of the investigation. Four days later, Davis talked with Starks again, and she discounted a circulating rumor that Virgil had heard a car outside their home several nights in a row and feared being killed.


title: Texarkana Moonlight Murders

text: Investigations of the attacks involved numerous law enforcement officers at the city, county, state and federal levels. Notable investigators include:


title: Texarkana Moonlight Murders

text: Law enforcement repeatedly challenged Larey's account of the first attack, and believed that she and Hollis knew the identity of their attacker and were covering for him. No suspects were apprehended. Larey returned to Texarkana after the Griffin-Moore murders in hopes of helping to link the cases and identify the killer, but the Texas Rangers questioned her story and insisted that she knew who her attacker was. Officers did not publicly connect the Hollis-Larey attack to the subsequent murders until May 11, the day after a "Texarkana Gazette" interview with Larey was published, when Presley and Runnels called on the public to immediately report anyone who had an unexplained absence on the nights of the four attacks.


title: Texarkana Moonlight Murders

text: In response to the Griffin-Moore murders, police launched a citywide investigation along with the Texas and Arkansas city police, the Texas Department of Public Safety (the overseeing agency of the Texas Rangers), Miller and Cass County sheriffs' departments, and the Federal Bureau of Investigation (FBI). Over 200 persons were questioned in the case, and about the same number of false leads were checked. Three people found with bloody clothing were taken into custody; all three were cleared of suspicion.


title: Texarkana Moonlight Murders

text: In the Martin-Booker case, friends, acquaintances, and several suspects were questioned in the Bowie Country building by officers who worked in 24-hour relays. Suspects were brought in from as far away as .


title: Texarkana Moonlight Murders

text: Gonzaullas tried baiting the Phantom by recruiting teenagers to sit as decoys in parked cars while officers waited nearby. Officers also volunteered as decoys, with real partners or mannequins. Following the Booker-Martin murders, some officers hid in trees at Spring Lake Park.


title: Texarkana Moonlight Murders

text: In the aftermath of the May 3 Starks murder, officers from the entire area were called upon to help in the investigation. Blockades were effected on Highway 67 East. Those who had been driving in the area near the time of the slaying, along with several men found in the vicinity, were detained for questioning. By May 5, forty-seven officers were working to solve the murder. On May 9, a mobile radio station arrived with twenty Arkansas state police officers and a fleet of ten prowl cars equipped with two-way radios, to help coordinate the growing investigation. On May 11, a teletype machine was installed in the Bowie County Sheriff's office to connect with other law-enforcement offices in Texas. The unofficial theory for a motive amongst the majority of officers was that of "sex mania", as large amounts of money in the home were not taken, nor was Katie Starks's purse.


title: Texarkana Moonlight Murders

text: By March 30, police had posted a $500 reward in an effort to gain any new information on the case, but this produced over 100 false leads with no fruitful clues or suspects. Within days of the Booker-Martin murders, the reward fund had exceeded $1,700. It rose to $7,025 on the night of the Starks murder and passed $10,000 in the following ten days.


title: Texarkana Moonlight Murders

text: There was some hesitation in linking the Starks murder to the other crimes, because the weapon used was a .22, and Davis believed it was an automatic rifle. By November 1948, authorities no longer considered the Starks murder connected to the two double-murders.


title: Texarkana Moonlight Murders

text: The Griffin-Moore murders raised public concerns but were generally taken as an isolated incident, as officials did not publicly connect the earlier Hollis-Larey attack to the murders while the Phantom Killer was active. The Martin-Booker murders thus greatly alarmed the public to the likelihood of a serial predator. The deaths of these two church-going teenagers shocked the community. Booker had been a popular high-school junior, a sorority member, an officer of her high school band, a winner of scholastic, literary and musical prizes, and a former Little Miss Texarkana. Her high school ended classes early so that hundreds of young people could attend the funerals. Curfews were set for businesses in an attempt to keep people off the streets at night. It was additionally at this point that the hypothesized serial killer was dubbed "The Phantom Killer" by local media.


title: Texarkana Moonlight Murders

text: Hysteria grew in the days following the murder of Virgil Starks in his home. There was constant media coverage of the increased police activity and the "Texarkana Gazette" stated on May 5 that the killer might strike again at any moment, at any place, and at anyone. For a week police were inundated with reports of prowlers. One officer stated that nearly all of the alarm was the result of excitement, wild imagination, and near-hysteria.


title: Texarkana Moonlight Murders

text: Previously, it had been normal for houses to be left unlocked. The murders alarmed residents into taking precautions with security: from locking doors to arming themselves with guns; some people nailed sheets over their windows, some nailed windows down and some used screen-door braces as window guards. The day after Starks's death, stores sold out of locks, guns, ammunition, window shades and Venetian blinds. Additional items of which sales increased included window sash locks, screen door hooks, night latches, and other protective devices. Guard dogs were sought in local want-ads.


title: Texarkana Moonlight Murders

text: Because citizens were considerably nervous and armed with guns, Texarkana became a dangerous place. When calling on an address, law enforcement officers would turn on their sirens, stand in their headlights, and announce themselves to keep from being shot by a nervous homeowner. Gonzaullas fuelled the hysteria when he announced on May 7 that citizens should "oil up their guns and see if they are loaded" and to "not hesitate" if they feel it necessary to use them.


title: Texarkana Moonlight Murders

text: The fear was significant enough to spread to other cities, including Hope, Lufkin, Magnolia, and as far as Oklahoma City, where there were sales spikes for guns and axes. After three weeks without an associated murder, Texarkana's fear began to lessen. The concern lasted throughout the summer and subsided after three months had passed.


title: Texarkana Moonlight Murders

text: The rampant spreading of rumors fed the panic and made the police investigations more difficult. On April 18, Gonzaullas held a press conference to dispel rumors that the murderer had been caught. He stated that the rumors circulating among the public and in the newspapers were "a hindrance to the investigation and harmful to innocent persons." He stressed this again in a radio interview on May 7: "[rumors] only take the officers from the main route of the investigation. It is so important that we capture this man that we cannot afford to overlook any lead, no matter how fantastic it may seem."


title: Texarkana Moonlight Murders

text: Rumors continued to be spread through mid-May. Many people believed that the slayer had been caught. Some believed he was being secretly held at the Bowie County Jail or flown to another jail. The "Gazette" and "News" offices were drowned with phone calls, both local and long distance, inquiring about the apprehension of the killer. Presley declared that innocent people were being accused of being the Phantom and asked residents to show more consideration for their fellow citizens.


title: Texarkana Moonlight Murders

text: Although most of the town was in fear of the Phantom, some youths continued parking on deserted roads, hoping to apprehend the perpetrator. Johnson and an Arkansas State Trooper were patrolling a vacant road at night when they came up to a parked car. When Johnson approached the car and noticed a couple, he introduced himself and asked if they weren't scared. The girl replied, "It's a good thing you told me who you are," and she revealed that she had been pointing a .25 ACP pistol at him.


title: Texarkana Moonlight Murders

text: On the night of May 10, Texarkana City Police officers were alerted to a car that had been following a bus. They chased it for before shooting the tires and arresting C. J. Lauderdale Jr., a high-school athlete. When questioned at the station, he explained that he was unaware they were policemen because they were driving an unmarked car. He said he was following the bus because he was suspicious of a passenger that had entered from a private car. On May 12, Gonzaullas gave a warning to "teenage sleuths" in the "Gazette", saying, "it's a good way to get killed."


title: Texarkana Moonlight Murders

text: The unidentified killer did not acquire a nickname until after the deaths of Booker and Martin. In the April 16 edition of the "Texarkana Daily News", a heading read "Phantom Killer Eludes Officers as Investigation of Slayings Pressed". This front-page story was continued on page two with the headline, "Phantom Slayer Eludes Police". The "Texarkana Gazette" contained a small title on April 17 which read, "Phantom Slayer Still at Large as Probe Continues". J. Q. Mahaffey, executive editor of the "Texarkana Gazette" in 1946, said that managing editor Calvin Sutton had an acute sense for the dramatic, which impelled him to ask if they could refer to the unknown murderer as "The Phantom". Mahaffey replied, "Why not? If the SOB continues to elude capture, he certainly can be called a phantom!"


title: Texarkana Moonlight Murders

text: Jimmy Hollis and Mary Jeanne Larey were the only victims able to give a description of their attacker. They described him as being tall, wearing a white mask over his face with holes cut out for his eyes and mouth. Although Hollis believed he was a young, dark-tanned, white man under 30 years old, Larey believed he was a light-skinned African American. With no description from the other incidents, it cannot be certain if the same perpetrator or perpetrators were responsible, though it is generally assumed that the crimes were the work of a single individual.


title: Texarkana Moonlight Murders

text: The modus operandi established for the killer was that he attacked young couples in empty or private areas just outside city limits using a .32 caliber gun. Although the caliber used in the Starks murder was a .22, a .32 was still believed by the majority of lawmen to have been used by the Phantom. He always attacked late at night on weekends, with cooling off periods of about three weeks between attacks.


title: Texarkana Moonlight Murders

text: Gonzaullas stated that he and his officers were dealing with a "shrewd criminal who had left no stone unturned to conceal his identity and activities," and that the murderer's efforts were both clever and baffling. He also stated that the man they were hunting was a "cunning individual who would go to all lengths to avoid apprehension."


title: Texarkana Moonlight Murders

text: At the Starks murder scene, Presley said, "This killer is the luckiest person I have ever known. No one sees him, hears him in time, or can identify him in any way." Officers have said that the killer is apparently a maniac who is an expert with a gun. Victim and survivor Hollis said, "I know he's crazy. The crazy things he said made me feel that his mind was warped."


title: Texarkana Moonlight Murders

text: Dr. Anthony Lapalla, a psychologist at the Federal Correctional Institution in Texarkana, believed at the time that the killer was planning to continue to make unexpected attacks such as that of Virgil Starks on the outskirts of town. He also believed that the same person committed all five murders, and that the killer was somewhere between his mid-30s and 50, apparently motivated by a strong sex drive and sadism. Lapella stated that a person who would commit such crimes was intelligent, clever, and shrewd, and often was not apprehended.


title: Texarkana Moonlight Murders

text: According to Lapalla's theories, the killer was not afraid of the police activity, but was aware of the increased difficulty of attacking people on vacant roads and so he had shifted his target to a farmhouse. He said that the killer could be leading a normal life, was unlikely a veteran, and was not necessarily a resident of the area despite his knowledge of it. He stated that the attacks show evidence of deep planning, that the killer works alone and tells no one of his crimes, and could either shift his crimes to a distant community or overcome the desire to assault and kill people. Lapalla did not believe the killer was a black man because "in general, negro criminals are not that clever."


title: Texarkana Moonlight Murders

text: There were numerous false confessions investigated by police. Tackett recalled nine people who confessed to being the Phantom, but their statements did not agree with the facts.


title: Texarkana Moonlight Murders

text: In the Griffin and Moore case, over 200 persons were questioned, and about the same number of false tips and leads were checked. Three suspects were taken into custody for bloody clothing, two of whom were released after officers received satisfying explanations. The remaining suspect was held in Vernon, Texas, for further investigation, but was later cleared of suspicion.


title: Texarkana Moonlight Murders

text: Youell Swinney was a 29-year-old car thief and counterfeiter. He was arrested in July by Tackett, who was investigating car thefts after realizing that on the night of the Griffin-Moore murders a car had been stolen in the area and a previously stolen car had been found abandoned. Tackett was able to locate the former car and arrested Swinney's wife Peggy when she came to retrieve it. Peggy confessed in great detail that Swinney was the Phantom Killer and had killed Booker and Martin. Her story changed in some details across several interviews, and police believed she was withholding information due to fear of Swinney or of incriminating herself.


title: Texarkana Moonlight Murders

text: Police were able to independently verify some details of Peggy's confession, such as the location of a victim's possessions where she said Youell had discarded them. There was considerable circumstantial evidence against Swinney, but Peggy's confession was the most critical part of the case. However, Peggy recanted her confession, was considered an unreliable witness, and could not be compelled to testify against her husband.


title: Texarkana Moonlight Murders

text: Law enforcement officers worked for six months trying to validate Peggy's confession and tie Swinney to the murders. They found that on the night of the Booker-Martin murders, the Swinneys were sleeping in their car under a bridge near San Antonio. Swinney was never charged with murder and was instead tried and imprisoned as a habitual offender for car theft. Presley reported in his 2014 book that investigators in the Swinney case later said that the sentence was effectively a plea bargain, though the case files indicated no formal agreement. Swinney was apparently concerned about being sentenced to death for the murders, so agreed to not contest the habitual offender charge and in fact tried to plead guilty despite the charge requiring a jury trial.


title: Texarkana Moonlight Murders

text: Henry Booker "Doodie" Tennison was an 18-year-old university freshman who died by suicide on November 4, 1948, leaving behind cryptic instructions which directed investigators to a suicide note in which Tennison confessed to the Booker, Martin, and Starks murders. He had played trombone in the same high-school band as Booker, but they were not friends. Investigators were unable to find any other evidence linking Tennison to the murders. James Freeman, a friend of Tennison, provided an alibi for the night of the Starks murder, stating that they had been playing cards that evening when they heard the news of the attack.


title: Texarkana Moonlight Murders

text: Ralph B. Baumann, a 21-year-old ex-Army Air Force (AAF) machine-gunner, claimed to have awoken from a fugue state of several weeks on the day of the Starks murder, with his rifle missing. He said that he heard about a suspect matching his description and hitchhiked to Los Angeles, feeling like he was running from murder. On May 23, he told Los Angeles police that he thought he might be the Phantom. "I'm my own suspect," he said.


title: Texarkana Moonlight Murders

text: Police arrested him but Gonzaullas stated that several parts of the man's story had little basis in fact. Baumann said that he'd been discharged from the AAF for being a psychoneurotic, and he had previously confessed to killing three people in Texarkana in a period of three days (which did not match the timeline of killings).


title: Texarkana Moonlight Murders

text: Investigators had hoped that Booker's saxophone, which she had played the night of her murder and which was missing, might lead them to a suspect. On April 27, a suspicious man was arrested in Corpus Christi, Texas, for trying to sell a saxophone to a music store. He had asked about selling the instrument to the store but became evasive and fled from the store manager." Although no saxophone was found in his possession, the police found a bag of bloody clothing in his hotel room. After several days of questioning, the man was cleared as a suspect. Booker's saxophone was located on October 24, six months after her murder, in underbrush near the place her body had been found.


title: Texarkana Moonlight Murders

text: On May 8, it was announced that an escaped German prisoner of war—who was already being hunted as "a matter of routine"—was considered a suspect. He was described as a stocky 24-year-old, weighing , with brown hair and blue eyes. He had stolen a car in Mount Ida, Arkansas, and attempted to buy ammunition in several eastern Oklahoma towns. The police kept searching for the POW, but it was said that he had "vanished into thin air."


title: Texarkana Moonlight Murders

text: On May 7, a hitchhiker armed with a pistol carjacked and robbed a man, threatening to kill him and stating that he had killed five people in Texarkana, naming Martin and Booker. The hitchhiker went on to say that he was not finished killing people. Gonzaullas said that police were doubtful that this man was the Phantom Killer, noting that the killer had gone to lengths to conceal his identity while the hitchhiker boasted to a living witness.


title: Texarkana Moonlight Murders

text: On May 10, in Atoka, Oklahoma, a man assaulted a woman in her home, ranting that he might as well kill her because he had already killed three or four people, and that he was going to rape her. He then fled. A widespread search for the man included 20 officers and 160 residents. Two days later, police arrested a suspect but did not believe this man was the Phantom. According to the man's story, he could not have been in Texarkana at the time of the Starks murder.


title: Texarkana Moonlight Murders

text: Sammie is a pseudonym given to a longtime Texarkana resident with a good reputation whom the police were reluctant to name as a suspect. His vehicle's tire tracks were found across the road from Martin's corpse. He failed a polygraph test so the police decided to have him hypnotized by psychiatrist Travis Elliott. Elliott concluded that Sammie had no criminal tendencies, that he had pulled his vehicle to the side of the road in order to urinate, and that he subsequently visited a married woman with whom he was having an affair—concealing this caused Sammie to fail the polygraph test. After police verified the details, they cleared Sammie as a suspect.


title: Texarkana Moonlight Murders

text: A taxi driver became a major suspect in the Booker-Marin murders because his cab was seen in the vicinity of the crime scene that morning, but he was soon cleared.


title: Texarkana Moonlight Murders

text: On May 7, at approximately 6 a.m., the body of Earl Cliff McSpadden was found on the Kansas City Southern Railway tracks north of Texarkana, near Ogden. The body's left arm and leg had been severed by a freight train a half-hour earlier. The coroner's jury's verdict stated, "death at the hands of persons unknown", and that "he was dead before being placed on the railroad tracks." Because the murder is unsolved, locals have speculated that McSpadden was the Phantom's sixth victim. A prominent rumor exists claiming that McSpadden was the Phantom, and had committed suicide by jumping in front of a train.


title: Won Jin-ah

text: Won Jin-ah (born March 29, 1991) is a South Korean actress known for her roles in "Rain or Shine" (2017) and "Life" (2018). She earned a Baeksang Arts Award nomination for "Rain or Shine".


title: Pressure measurement

text: Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges, vacuum gauges or compound gauges (vacuum & pressure). The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.


title: Pressure measurement

text: A vacuum gauge is used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (for instance, −1 bar or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very low pressures, a gauge that uses total vacuum as the zero point reference must be used, giving pressure reading as an absolute pressure.


title: Pressure measurement

text: Other methods of pressure measurement involve sensors that can transmit the pressure reading to a remote indicator or control system (telemetry).


title: Pressure measurement

text: Everyday pressure measurements, such as for vehicle tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other specific reference. When distinguishing between these zero references, the following terms are used:


title: Pressure measurement

text: The zero reference in use is usually implied by context, and these words are added only when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute.


title: Pressure measurement

text: For most working fluids where a fluid exists in a closed system, gauge pressure measurement prevails. Pressure instruments connected to the system will indicate pressures relative to the current atmospheric pressure. The situation changes when extreme vacuum pressures are measured, then absolute pressures are typically used instead and measuring instruments used will be different.


title: Pressure measurement

text: Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings.


title: Pressure measurement

text: Moderate vacuum pressure readings can be ambiguous without the proper context, as they may represent absolute pressure or gauge pressure without a negative sign. Thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 4 inHg, calculated as 30 inHg (typical atmospheric pressure) − 26 inHg (gauge pressure).


title: Pressure measurement

text: Atmospheric pressure is typically about 100 kPa at sea level, but is variable with altitude and weather. If the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes. For example, when a car drives up a mountain, the (gauge) tire pressure goes up because atmospheric pressure goes down. The absolute pressure in the tire is essentially unchanged.


title: Pressure measurement

text: Using atmospheric pressure as reference is usually signified by a "g" for gauge after the pressure unit, e.g. 70 psig, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg).


title: Pressure measurement

text: A vented-gauge pressure transmitter, for example, allows the outside air pressure to be exposed to the negative side of the pressure-sensing diaphragm, through a vented cable or a hole on the side of the device, so that it always measures the pressure referred to ambient barometric pressure. Thus a vented-gauge reference pressure sensor should always read zero pressure when the process pressure connection is held open to the air.


title: Pressure measurement

text: A sealed gauge reference is very similar, except that atmospheric pressure is sealed on the negative side of the diaphragm. This is usually adopted on high pressure ranges, such as hydraulics, where atmospheric pressure changes will have a negligible effect on the accuracy of the reading, so venting is not necessary. This also allows some manufacturers to provide secondary pressure containment as an extra precaution for pressure equipment safety if the burst pressure of the primary pressure sensing diaphragm is exceeded.


title: Pressure measurement

text: There is another way of creating a sealed gauge reference, and this is to seal a high vacuum on the reverse side of the sensing diaphragm. Then the output signal is offset, so the pressure sensor reads close to zero when measuring atmospheric pressure.


title: Pressure measurement

text: A sealed gauge reference pressure transducer will never read exactly zero because atmospheric pressure is always changing and the reference in this case is fixed at 1 bar.


title: Pressure measurement

text: To produce an absolute pressure sensor, the manufacturer seals a high vacuum behind the sensing diaphragm. If the process-pressure connection of an absolute-pressure transmitter is open to the air, it will read the actual barometric pressure.


title: Pressure measurement

text: For much of human history, the pressure of gases like air was ignored, denied, or taken for granted, but as early as the 6th century BC, Greek philosopher Anaximenes of Miletus claimed that all things are made of air that is simply changed by varying levels of pressure. He could observe water evaporating, changing to a gas, and felt that this applied even to solid matter. More condensed air made colder, heavier objects, and expanded air made lighter, hotter objects. This was akin to how gases really do become less dense when warmer, more dense when cooler.


title: Pressure measurement

text: In the 17th century, Evangelista Torricelli conducted experiments with mercury that allowed him to measure the presence of air. He would dip a glass tube, closed at one end, into a bowl of mercury and raise the closed end up out of it, keeping the open end submerged. The weight of the mercury would pull it down, leaving a partial vacuum at the far end. This validated his belief that air/gas has mass, creating pressure on things around it. Previously, the more popular conclusion, even for Galileo, was that air was weightless and it is vacuum that provided force, as in a siphon. The discovery helped bring Torricelli to the conclusion:


title: Pressure measurement

text: Blaise Pascal went farther, having his brother-in-law try the experiment at different altitudes on a mountain, and finding indeed that the farther down in the ocean of atmosphere, the higher the pressure.


title: Pressure measurement

text: The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N·m or kg·m·s). This special name for the unit was added in 1971; before that, pressure in SI was expressed in units such as N·m. When indicated, the zero reference is stated in parenthesis following the unit, for example 101 kPa (abs). The pound per square inch (psi) is still in widespread use in the US and Canada, for measuring, for instance, tire pressure. A letter is often appended to the psi unit to indicate the measurement's zero reference; psia for absolute, psig for gauge, psid for differential, although this practice is discouraged by the NIST.


title: Pressure measurement

text: Because pressure was once commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid ("e.g.," inches of water). Manometric measurement is the subject of pressure head calculations. The most common choices for a manometer's fluid are mercury (Hg) and water; water is nontoxic and readily available, while mercury's density allows for a shorter column (and so a smaller manometer) to measure a given pressure. The abbreviation "W.C." or the words "water column" are often printed on gauges and measurements that use water for the manometer.


title: Pressure measurement

text: Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. So measurements in "millimetres of mercury" or "inches of mercury" can be converted to SI units as long as attention is paid to the local factors of fluid density and gravity. Temperature fluctuations change the value of fluid density, while location can affect gravity.


title: Pressure measurement

text: Although no longer preferred, these manometric units are still encountered in many fields. Blood pressure is measured in millimetres of mercury (see torr) in most of the world, central venous pressure and lung pressures in centimeters of water are still common, as in settings for CPAP machines. Natural gas pipeline pressures are measured in inches of water, expressed as "inches W.C."


title: Pressure measurement

text: Underwater divers use manometric units: the ambient pressure is measured in units of metres sea water (msw) which is defined as equal to one tenth of a bar. The unit used in the US is the foot sea water (fsw), based on standard gravity and a sea-water density of 64 lb/ft. According to the US Navy Diving Manual, one fsw equals 0.30643 msw, , or , though elsewhere it states that 33 fsw is (one atmosphere), which gives one fsw equal to about 0.445 psi. The msw and fsw are the conventional units for measurement of diver pressure exposure used in decompression tables and the unit of calibration for pneumofathometers and hyperbaric chamber pressure gauges. Both msw and fsw are measured relative to normal atmospheric pressure.


title: Pressure measurement

text: In vacuum systems, the units torr (millimeter of mercury), micron (micrometer of mercury), and inch of mercury (inHg) are most commonly used. Torr and micron usually indicates an absolute pressure, while inHg usually indicates a gauge pressure.


title: Pressure measurement

text: Atmospheric pressures are usually stated using hectopascal (hPa), kilopascal (kPa), millibar (mbar) or atmospheres (atm). In American and Canadian engineering, stress is often measured in kip. Note that stress is not a true pressure since it is not scalar. In the cgs system the unit of pressure was the barye (ba), equal to 1 dyn·cm. In the mts system, the unit of pressure was the pieze, equal to 1 sthene per square metre.


title: Pressure measurement

text: Many other hybrid units are used such as mmHg/cm or grams-force/cm (sometimes as kg/cm without properly identifying the force units). Using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force is prohibited in SI; the unit of force in SI is the newton (N).


title: Pressure measurement

text: Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure.


title: Pressure measurement

text: While static gauge pressure is of primary importance to determining net loads on pipe walls, dynamic pressure is used to measure flow rates and airspeed. Dynamic pressure can be measured by taking the differential pressure between instruments parallel and perpendicular to the flow. Pitot-static tubes, for example perform this measurement on airplanes to determine airspeed. The presence of the measuring instrument inevitably acts to divert flow and create turbulence, so its shape is critical to accuracy and the calibration curves are often non-linear.


title: Pressure measurement

text: Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column (a vertical tube filled with mercury) manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christiaan Huygens in 1661.


title: Pressure measurement

text: Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration. They have poor dynamic response.


title: Pressure measurement

text: Piston-type gauges counterbalance the pressure of a fluid with a spring (for example tire-pressure gauges of comparatively low accuracy) or a solid weight, in which case it is known as a deadweight tester and may be used for calibration of other gauges.


title: Pressure measurement

text: Liquid-column gauges consist of a column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight (a force applied due to gravity) is in equilibrium with the pressure differential between the two ends of the tube (a force applied due to fluid pressure). A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which might be the atmospheric pressure or a vacuum) is applied to the other. The difference in liquid levels represents the applied pressure. The pressure exerted by a column of fluid of height "h" and density "ρ" is given by the hydrostatic pressure equation, "P" = "hgρ". Therefore, the pressure difference between the applied pressure "P" and the reference pressure "P" in a U-tube manometer can be found by solving . In other words, the pressure on either end of the liquid (shown in blue in the figure) must be balanced (since the liquid is static), and so .


title: Pressure measurement

text: In most liquid-column measurements, the result of the measurement is the height "h", expressed typically in mm, cm, or inches. The "h" is also known as the pressure head. When expressed as a pressure head, pressure is specified in units of length and the measurement fluid must be specified. When accuracy is critical, the temperature of the measurement fluid must likewise be specified, because liquid density is a function of temperature. So, for example, pressure head might be written "742.2 mm" or "4.2 in at 59 °F" for measurements taken with mercury or water as the manometric fluid respectively. The word "gauge" or "vacuum" may be added to such a measurement to distinguish between a pressure above or below the atmospheric pressure. Both mm of mercury and inches of water are common pressure heads, which can be converted to S.I. units of pressure using unit conversion and the above formulas.


title: Pressure measurement

text: If the fluid being measured is significantly dense, hydrostatic corrections may have to be made for the height between the moving surface of the manometer working fluid and the location where the pressure measurement is desired, except when measuring differential pressure of a fluid (for example, across an orifice plate or venturi), in which case the density ρ should be corrected by subtracting the density of the fluid being measured.


title: Pressure measurement

text: Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm) and low vapour pressure. Its convex meniscus is advantageous since this means there will be no pressure errors from wetting the glass, though under exceptionally clean circumstances, the mercury will stick to glass and the barometer may become stuck (the mercury can sustain a negative absolute pressure) even under a strong vacuum. For low pressure differences, light oil or water are commonly used (the latter giving rise to units of measurement such as inches water gauge and millimetres HO). Liquid-column pressure gauges have a highly linear calibration. They have poor dynamic response because the fluid in the column may react slowly to a pressure change.


title: Pressure measurement

text: When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a loop filled with gas or a light fluid can isolate the liquids to prevent them from mixing, but this can be unnecessary, for example, when mercury is used as the manometer fluid to measure differential pressure of a fluid such as water. Simple hydrostatic gauges can measure pressures ranging from a few torrs (a few 100 Pa) to a few atmospheres (approximately ).


title: Pressure measurement

text: A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Based on the use and structure, following types of manometers are used


title: Pressure measurement

text: A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few millimetres of mercury. The technique is very slow and unsuited to continual monitoring, but is capable of good accuracy. Unlike other manometer gauges, the McLeod gauge reading is dependent on the composition of the gas, since the interpretation relies on the sample compressing as an ideal gas. Due to the compression process, the McLeod gauge completely ignores partial pressures from non-ideal vapors that condense, such as pump oils, mercury, and even water if compressed enough.


title: Pressure measurement

text: 0.1 mPa is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-dependent properties. These indirect measurements must be calibrated to SI units by a direct measurement, most commonly a McLeod gauge.


title: Pressure measurement

text: Aneroid gauges are based on a metallic pressure-sensing element that flexes elastically under the effect of a pressure difference across the element. "Aneroid" means "without fluid", and the term originally distinguished these gauges from the hydrostatic gauges described above. However, aneroid gauges can be used to measure the pressure of a liquid as well as a gas, and they are not the only type of gauge that can operate without fluid. For this reason, they are often called mechanical gauges in modern language. Aneroid gauges are not dependent on the type of gas being measured, unlike thermal and ionization gauges, and are less likely to contaminate the system than hydrostatic gauges. The pressure sensing element may be a Bourdon tube, a diaphragm, a capsule, or a set of bellows, which will change shape in response to the pressure of the region in question. The deflection of the pressure sensing element may be read by a linkage connected to a needle, or it may be read by a secondary transducer. The most common secondary transducers in modern vacuum gauges measure a change in capacitance due to the mechanical deflection. Gauges that rely on a change in capacitance are often referred to as capacitance manometers.


title: Pressure measurement

text: The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. (A party horn illustrates this principle.) This change in cross-section may be hardly noticeable, involving moderate stresses within the elastic range of easily workable materials. The strain of the material of the tube is magnified by forming the tube into a C shape or even a helix, such that the entire tube tends to straighten out or uncoil elastically as it is pressurized. Eugène Bourdon patented his gauge in France in 1849, and it was widely adopted because of its superior simplicity, linearity, and accuracy; Bourdon is now part of the Baumer group and still manufacture Bourdon tube gauges in France. Edward Ashcroft purchased Bourdon's American patent rights in 1852 and became a major manufacturer of gauges. Also in 1849, Bernard Schaeffer in Magdeburg, Germany patented a successful diaphragm (see below) pressure gauge, which, together with the Bourdon gauge, revolutionized pressure measurement in industry. But in 1875 after Bourdon's patents expired, his company Schaeffer and Budenberg also manufactured Bourdon tube gauges.


title: Pressure measurement

text: In practice, a flattened thin-wall, closed-end tube is connected at the hollow end to a fixed pipe containing the fluid pressure to be measured. As the pressure increases, the closed end moves in an arc, and this motion is converted into the rotation of a (segment of a) gear by a connecting link that is usually adjustable. A small-diameter pinion gear is on the pointer shaft, so the motion is magnified further by the gear ratio. The positioning of the indicator card behind the pointer, the initial pointer shaft position, the linkage length and initial position, all provide means to calibrate the pointer to indicate the desired range of pressure for variations in the behavior of the Bourdon tube itself. Differential pressure can be measured by gauges containing two different Bourdon tubes, with connecting linkages (but is more usually measured via diaphragms or bellows and a balance system).


title: Pressure measurement

text: Bourdon tubes measures gauge pressure, relative to ambient atmospheric pressure, as opposed to absolute pressure; vacuum is sensed as a reverse motion. Some aneroid barometers use Bourdon tubes closed at both ends (but most use diaphragms or capsules, see below). When the measured pressure is rapidly pulsing, such as when the gauge is near a reciprocating pump, an orifice restriction in the connecting pipe is frequently used to avoid unnecessary wear on the gears and provide an average reading; when the whole gauge is subject to mechanical vibration, the case (including the pointer and dial) can be filled with an oil or glycerin. Typical high-quality modern gauges provide an accuracy of ±1% of span (Nominal diameter 100mm, Class 1 EN837-1), and a special high-accuracy gauge can be as accurate as 0.1% of full scale.


title: Pressure measurement

text: Force-balanced fused quartz Bourdon tube sensors work on the same principle but uses the reflection of a beam of light from a mirror to sense the angular displacement and current is applied to electromagnets to balance the force of the tube and bring the angular displacement back to zero, the current that is applied to the coils is used as the measurement. Due to the extremely stable and repeatable mechanical and thermal properties of quartz and the force balancing which eliminates nearly all physical movement these sensors can be accurate to around 1 PPM of full scale. Due to the extremely fine fused quartz structures which must be made by hand these sensors are generally limited to scientific and calibration purposes.


title: Pressure measurement

text: In the following illustrations of a compound gauge (vacuum and gauge pressure), the case and window has been removed to show only the dial, pointer and process connection. This particular gauge is a combination vacuum and pressure gauge used for automotive diagnosis:


title: Pressure measurement

text: A second type of aneroid gauge uses deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used.


title: Pressure measurement

text: In gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid. (Early barometers used a column of liquid such as water or the liquid metal mercury suspended by a vacuum.) This bellows configuration is used in aneroid barometers (barometers with an indicating needle and dial card), altimeters, altitude recording barographs, and the altitude telemetry instruments used in weather balloon radiosondes. These devices use the sealed chamber as a reference pressure and are driven by the external pressure. Other sensitive aircraft instruments such as air speed indicators and rate of climb indicators (variometers) have connections both to the internal part of the aneroid chamber and to an external enclosing chamber.


title: Pressure measurement

text: These gauges use the attraction of two magnets to translate differential pressure into motion of a dial pointer. As differential pressure increases, a magnet attached to either a piston or rubber diaphragm moves. A rotary magnet that is attached to a pointer then moves in unison. To create different pressure ranges, the spring rate can be increased or decreased.


title: Pressure measurement

text: The spinning-rotor gauge works by measuring how a rotating ball is slowed by the viscosity of the gas being measured. The ball is made of steel and is magnetically levitated inside a steel tube closed at one end and exposed to the gas to be measured at the other. The ball is brought up to speed (about 2500 or 3800 rad/s), and the deceleration rate is measured after switching off the drive, by electromagnetic transducers. The range of the instrument is 5 to 10 Pa (10 Pa with less accuracy). It is accurate and stable enough to be used as a secondary standard. During the last years this type of gauge became much more user friendly and easier to operate. In the past the instrument was famous to requires some skill and knowledge to use correctly. For high accuracy measurements various corrections must be applied and the ball must be spun at a pressure well below the intended measurement pressure for five hours before using. It is most useful in calibration and research laboratories where high accuracy is required and qualified technicians are available. Insulation vacuum monitoring of cryogenic liquids is a perfect suited application for this system too. With the inexpensive and long term stable, weldable sensor, that can be separated from the more costly electronics/read it is a perfect fit to all static vacuums.


title: Pressure measurement

text: This is an over-simplified diagram, but you can see the fundamental design of the internal ports in the sensor. The important item here to note is the "diaphragm" as this is the sensor itself. Please note that is it slightly convex in shape (highly exaggerated in the drawing); this is important as it affects the accuracy of the sensor in use.


title: Pressure measurement

text: Generally, as a real gas increases in density -which may indicate an increase in pressure- its ability to conduct heat increases. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or resistance thermometer (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge, which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 Torr to 10 Torr, but their calibration is sensitive to the chemical composition of the gases being measured.


title: Pressure measurement

text: A Pirani gauge consists of a metal wire open to the pressure being measured. The wire is heated by a current flowing through it and cooled by the gas surrounding it. If the gas pressure is reduced, the cooling effect will decrease, hence the equilibrium temperature of the wire will increase. The resistance of the wire is a function of its temperature: by measuring the voltage across the wire and the current flowing through it, the resistance (and so the gas pressure) can be determined. This type of gauge was invented by Marcello Pirani.


title: Pressure measurement

text: In two-wire gauges, one wire coil is used as a heater, and the other is used to measure temperature due to convection. Thermocouple gauges and thermistor gauges work in this manner using a thermocouple or thermistor, respectively, to measure the temperature of the heated wire.


title: Pressure measurement

text: Ionization gauges are the most sensitive gauges for very low pressures (also referred to as hard or high vacuum). They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. The calibration of an ion gauge is unstable and dependent on the nature of the gases being measured, which is not always known. They can be calibrated against a McLeod gauge which is much more stable and independent of gas chemistry.


title: Pressure measurement

text: Thermionic emission generates electrons, which collide with gas atoms and generate positive ions. The ions are attracted to a suitably biased electrode known as the collector. The current in the collector is proportional to the rate of ionization, which is a function of the pressure in the system. Hence, measuring the collector current gives the gas pressure. There are several sub-types of ionization gauge.


title: Pressure measurement

text: Most ion gauges come in two types: hot cathode and cold cathode. In the hot cathode version, an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 10 Torr to 10 Torr. The principle behind cold cathode version is the same, except that electrons are produced in the discharge of a high voltage. Cold cathode gauges are accurate from 10 Torr to 10 Torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.


title: Pressure measurement

text: A hot-cathode ionization gauge is composed mainly of three electrodes acting together as a triode, wherein the cathode is the filament. The three electrodes are a collector or plate, a filament, and a grid. The collector current is measured in picoamperes by an electrometer. The filament voltage to ground is usually at a potential of 30 volts, while the grid voltage at 180–210 volts DC, unless there is an optional electron bombardment feature, by heating the grid, which may have a high potential of approximately 565 volts.


title: Pressure measurement

text: The most common ion gauge is the hot-cathode Bayard–Alpert gauge, with a small ion collector inside the grid. A glass envelope with an opening to the vacuum can surround the electrodes, but usually the nude gauge is inserted in the vacuum chamber directly, the pins being fed through a ceramic plate in the wall of the chamber. Hot-cathode gauges can be damaged or lose their calibration if they are exposed to atmospheric pressure or even low vacuum while hot. The measurements of a hot-cathode ionization gauge are always logarithmic.


title: Pressure measurement

text: Electrons emitted from the filament move several times in back-and-forth movements around the grid before finally entering the grid. During these movements, some electrons collide with a gaseous molecule to form a pair of an ion and an electron (electron ionization). The number of these ions is proportional to the gaseous molecule density multiplied by the electron current emitted from the filament, and these ions pour into the collector to form an ion current. Since the gaseous molecule density is proportional to the pressure, the pressure is estimated by measuring the ion current.


title: Pressure measurement

text: The low-pressure sensitivity of hot-cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce x-rays that produce photoelectric noise in the ion collector. This limits the range of older hot-cathode gauges to 10 Torr and the Bayard–Alpert to about 10 Torr. Additional wires at cathode potential in the line of sight between the ion collector and the grid prevent this effect. In the extraction type the ions are not attracted by a wire, but by an open cone. As the ions cannot decide which part of the cone to hit, they pass through the hole and form an ion beam. This ion beam can be passed on to a:


title: Pressure measurement

text: There are two subtypes of cold-cathode ionization gauges: the Penning gauge (invented by Frans Michel Penning), and the inverted magnetron, also called a Redhead gauge. The major difference between the two is the position of the anode with respect to the cathode. Neither has a filament, and each may require a DC potential of about 4 kV for operation. Inverted magnetrons can measure down to 1  Torr.


title: Pressure measurement

text: Likewise, cold-cathode gauges may be reluctant to start at very low pressures, in that the near-absence of a gas makes it difficult to establish an electrode current - in particular in Penning gauges, which use an axially symmetric magnetic field to create path lengths for electrons that are of the order of metres. In ambient air, suitable ion-pairs are ubiquitously formed by cosmic radiation; in a Penning gauge, design features are used to ease the set-up of a discharge path. For example, the electrode of a Penning gauge is usually finely tapered to facilitate the field emission of electrons.


title: Pressure measurement

text: Maintenance cycles of cold cathode gauges are, in general, measured in years, depending on the gas type and pressure that they are operated in. Using a cold cathode gauge in gases with substantial organic components, such as pump oil fractions, can result in the growth of delicate carbon films and shards within the gauge that eventually either short-circuit the electrodes of the gauge or impede the generation of a discharge path.


title: Pressure measurement

text: When fluid flows are not in equilibrium, local pressures may be higher or lower than the average pressure in a medium. These disturbances propagate from their source as longitudinal pressure variations along the path of propagation. This is also called sound. Sound pressure is the instantaneous local pressure deviation from the average pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The effective sound pressure is the root mean square of the instantaneous sound pressure over a given interval of time. Sound pressures are normally small and are often expressed in units of microbar.


title: Pressure measurement

text: The American Society of Mechanical Engineers (ASME) has developed two separate and distinct standards on pressure measurement, B40.100 and PTC 19.2. B40.100 provides guidelines on Pressure Indicated Dial Type and Pressure Digital Indicating Gauges, Diaphragm Seals, Snubbers, and Pressure Limiter Valves. PTC 19.2 provides instructions and guidance for the accurate determination of pressure values in support of the ASME Performance Test Codes. The choice of method, instruments, required calculations, and corrections to be applied depends on the purpose of the measurement, the allowable uncertainty, and the characteristics of the equipment being tested.


title: Pressure measurement

text: The methods for pressure measurement and the protocols used for data transmission are also provided. Guidance is given for setting up the instrumentation and determining the uncertainty of the measurement. Information regarding the instrument type, design, applicable pressure range, accuracy, output, and relative cost is provided. Information is also provided on pressure-measuring devices that are used in field environments i.e., piston gauges, manometers, and low-absolute-pressure (vacuum) instruments.


title: Pressure measurement

text: These methods are designed to assist in the evaluation of measurement uncertainty based on current technology and engineering knowledge, taking into account published instrumentation specifications and measurement and application techniques. This Supplement provides guidance in the use of methods to establish the pressure-measurement uncertainty.


title: Chatbot

text: A chatbot or chatterbot is a software application used to conduct an on-line chat conversation via text or text-to-speech, in lieu of providing direct contact with a live human agent. Designed to convincingly simulate the way a human would behave as a conversational partner, chatbot systems typically require continuous tuning and testing, and many in production remain unable to adequately converse, while none of them can pass the standard Turing test. The term "ChatterBot" was originally coined by Michael Mauldin (creator of the first Verbot) in 1994 to describe these conversational programs.


title: Chatbot

text: Chatbots are used in dialog systems for various purposes including customer service, request routing, or information gathering. While some chatbot applications use extensive word-classification processes, natural-language processors, and sophisticated AI, others simply scan for general keywords and generate responses using common phrases obtained from an associated library or database.


title: Chatbot

text: Most chatbots are accessed on-line via website popups or through virtual assistants. They can be classified into usage categories that include: commerce (e-commerce via chat), education, entertainment, finance, health, news, and productivity.


title: Chatbot

text: In 1950, Alan Turing's famous article "Computing Machinery and Intelligence" was published, which proposed what is now called the Turing test as a criterion of intelligence. This criterion depends on the ability of a computer program to impersonate a human in a real-time written conversation with a human judge to the extent that the judge is unable to distinguish reliably—on the basis of the conversational content alone—between the program and a real human. The notoriety of Turing's proposed test stimulated great interest in Joseph Weizenbaum's program ELIZA, published in 1966, which seemed to be able to fool users into believing that they were conversing with a real human. However Weizenbaum himself did not claim that ELIZA was genuinely intelligent, and the introduction to his paper presented it more as a debunking exercise:


title: Chatbot

text: [In] artificial intelligence ... machines are made to behave in wondrous ways, often sufficient to dazzle even the most experienced observer. But once a particular program is unmasked, once its inner workings are explained ... its magic crumbles away; it stands revealed as a mere collection of procedures ... The observer says to himself "I could have written that". With that thought, he moves the program in question from the shelf marked "intelligent", to that reserved for curios ... The object of this paper is to cause just such a re-evaluation of the program about to be "explained". Few programs ever needed it more.


title: Chatbot

text: ELIZA's key method of operation (copied by chatbot designers ever since) involves the recognition of clue words or phrases in the input, and the output of the corresponding pre-prepared or pre-programmed responses that can move the conversation forward in an apparently meaningful way (e.g. by responding to any input that contains the word 'MOTHER' with 'TELL ME MORE ABOUT YOUR FAMILY'). Thus an illusion of understanding is generated, even though the processing involved has been merely superficial. ELIZA showed that such an illusion is surprisingly easy to generate because human judges are so ready to give the benefit of the doubt when conversational responses are "capable of being interpreted" as "intelligent".


title: Chatbot

text: Interface designers have come to appreciate that humans' readiness to interpret computer output as genuinely conversational—even when it is actually based on rather simple pattern-matching—can be exploited for useful purposes. Most people prefer to engage with programs that are human-like, and this gives chatbot-style techniques a potentially useful role in interactive systems that need to elicit information from users, as long as that information is relatively straightforward and falls into predictable categories. Thus, for example, online help systems can usefully employ chatbot techniques to identify the area of help that users require, potentially providing a "friendlier" interface than a more formal search or menu system. This sort of usage holds the prospect of moving chatbot technology from Weizenbaum's "shelf ... reserved for curios" to that marked "genuinely useful computational methods".


title: Chatbot

text: Among the most notable early chatbots are ELIZA (1966) and PARRY (1972). More recent notable programs include A.L.I.C.E., Jabberwacky and D.U.D.E (Agence Nationale de la Recherche and CNRS 2006). While ELIZA and PARRY were used exclusively to simulate typed conversation, many chatbots now include other functional features, such as games and web searching abilities. In 1984, a book called "The Policeman's Beard is Half Constructed" was published, allegedly written by the chatbot Racter (though the program as released would not have been capable of doing so).


title: Chatbot

text: One pertinent field of AI research is natural-language processing. Usually, weak AI fields employ specialized software or programming languages created specifically for the narrow function required. For example, A.L.I.C.E. uses a markup language called AIML, which is specific to its function as a conversational agent, and has since been adopted by various other developers of, so-called, Alicebots. Nevertheless, A.L.I.C.E. is still purely based on pattern matching techniques without any reasoning capabilities, the same technique ELIZA was using back in 1966. This is not strong AI, which would require sapience and logical reasoning abilities.


title: Chatbot

text: Jabberwacky learns new responses and context based on real-time user interactions, rather than being driven from a static database. Some more recent chatbots also combine real-time learning with evolutionary algorithms that optimize their ability to communicate based on each conversation held. Still, there is currently no general purpose conversational artificial intelligence, and some software developers focus on the practical aspect, information retrieval.


title: Chatbot

text: Chatbot competitions focus on the Turing test or more specific goals. Two such annual contests are the Loebner Prize and The Chatterbox Challenge (the latter has been offline since 2015, however, materials can still be found from web archives).


title: Chatbot

text: In November 2022, OpenAI developed an AI chatbot called ChatGPT which interacts using conversation to the general public and has garnered attention for its detailed responses and historical knowledge, although its accuracy has been criticized.


title: Chatbot

text: Many companies' chatbots run on messaging apps or simply via SMS. They are used for B2C customer service, sales and marketing.


title: Chatbot

text: In 2016, Facebook Messenger allowed developers to place chatbots on their platform. There were 30,000 bots created for Messenger in the first six months, rising to 100,000 by September 2017.


title: Chatbot

text: Since September 2017, this has also been as part of a pilot program on WhatsApp. Airlines KLM and Aeroméxico both announced their participation in the testing; both airlines had previously launched customer services on the Facebook Messenger platform.


title: Chatbot

text: The bots usually appear as one of the user's contacts, but can sometimes act as participants in a group chat.


title: Chatbot

text: Many banks, insurers, media companies, e-commerce companies, airlines, hotel chains, retailers, health care providers, government entities and restaurant chains have used chatbots to answer simple questions, increase customer engagement, for promotion, and to offer additional ways to order from them.


title: Chatbot

text: A 2017 study showed 4% of companies used chatbots. According to a 2016 study, 80% of businesses said they intended to have one by 2020.


title: Chatbot

text: Previous generations of chatbots were present on company websites, e.g. Ask Jenn from Alaska Airlines which debuted in 2008 or Expedia's virtual customer service agent which launched in 2011. The newer generation of chatbots includes IBM Watson-powered "Rocky", introduced in February 2017 by the New York City-based e-commerce company Rare Carat to provide information to prospective diamond buyers.


title: Chatbot

text: Used by marketers to script sequences of messages, very similar to an Autoresponder sequence. Such sequences can be triggered by user opt-in or the use of keywords within user interactions. After a trigger occurs a sequence of messages is delivered until the next anticipated user response. Each user response is used in the decision tree to help the chatbot navigate the response sequences to deliver the correct response message.


title: Chatbot

text: Other companies explore ways they can use chatbots internally, for example for Customer Support, Human Resources, or even in Internet-of-Things (IoT) projects. Overstock.com, for one, has reportedly launched a chatbot named Mila to automate certain simple yet time-consuming processes when requesting sick leave. Other large companies such as Lloyds Banking Group, Royal Bank of Scotland, Renault and Citroën are now using automated online assistants instead of call centres with humans to provide a first point of contact. A SaaS chatbot business ecosystem has been steadily growing since the F8 Conference when Facebook's Mark Zuckerberg unveiled that Messenger would allow chatbots into the app. In large companies, like in hospitals and aviation organizations, IT architects are designing reference architectures for Intelligent Chatbots that are used to unlock and share knowledge and experience in the organization more efficiently, and reduce the errors in answers from expert service desks significantly. These Intelligent Chatbots make use of all kinds of artificial intelligence like image moderation and natural-language understanding (NLU), natural-language generation (NLG), machine learning and deep learning.


title: Chatbot

text: Many high-tech banking organizations are looking to integrate automated AI-based solutions such as chatbots into their customer service in order to provide faster and cheaper assistance to their clients who are becoming increasingly comfortable with technology. In particular, chatbots can efficiently conduct a dialogue, usually replacing other communication tools such as email, phone, or SMS. In banking, their major application is related to quick customer service answering common requests, as well as transactional support.


title: Chatbot

text: Several studies report significant reduction in the cost of customer services, expected to lead to billions of dollars of economic savings in the next ten years. In 2019, Gartner predicted that by 2021, 15% of all customer service interactions globally will be handled completely by AI. A study by Juniper Research in 2019 estimates retail sales resulting from chatbot-based interactions will reach $112 billion by 2023.


title: Chatbot

text: Since 2016, when Facebook allowed businesses to deliver automated customer support, e-commerce guidance, content, and interactive experiences through chatbots, a large variety of chatbots were developed for the Facebook Messenger platform.


title: Chatbot

text: In 2016, Russia-based Tochka Bank launched the world's first Facebook bot for a range of financial services, including a possibility of making payments.


title: Chatbot

text: In July 2016, Barclays Africa also launched a Facebook chatbot, making it the first bank to do so in Africa.


title: Chatbot

text: The France's third-largest bank by total assets Société Générale launched their chatbot called SoBot in March 2018. While 80% of users of the SoBot expressed their satisfaction after having tested it, Société Générale deputy director Bertrand Cozzarolo stated that it will never replace the expertise provided by a human advisor.


title: Chatbot

text: The advantages of using chatbots for customer interactions in banking include cost reduction, financial advice, and 24/7 support.


title: Chatbot

text: Chatbots are also appearing in the healthcare industry. A study suggested that physicians in the United States believed that chatbots would be most beneficial for scheduling doctor appointments, locating health clinics, or providing medication information.


title: Chatbot

text: Whatsapp has teamed up with the World Health Organisation (WHO) to make a chatbot service that answers users’ questions on COVID-19.


title: Chatbot

text: In 2020, The Indian Government launched a chatbot called MyGov Corona Helpdesk, that worked through Whatsapp and helped people access information about the Coronavirus (COVID-19) pandemic. In the Philippines, the Medical City Clinic chatbot handles 8400+ chats a month, reducing wait times, including more native Tagalog and Cebuano speakers and improving overall patient experience.


title: Chatbot

text: Certain patient groups are still reluctant to use chatbots. A mixed-methods study showed that people are still hesitant to use chatbots for their healthcare due to poor understanding of the technological complexity, the lack of empathy, and concerns about cyber-security. The analysis showed that while 6% had heard of a health chatbot and 3% had experience of using it, 67% perceived themselves as likely to use one within 12 months. The majority of participants would use a health chatbot for seeking general health information (78%), booking a medical appointment (78%), and looking for local health services (80%). However, a health chatbot was perceived as less suitable for seeking results of medical tests and seeking specialist advice such as sexual health. The analysis of attitudinal variables showed that most participants reported their preference for discussing their health with doctors (73%) and having access to reliable and accurate health information (93%). While 80% were curious about new technologies that could improve their health, 66% reported only seeking a doctor when experiencing a health problem and 65% thought that a chatbot was a good idea. Interestingly, 30% reported dislike about talking to computers, 41% felt it would be strange to discuss health matters with a chatbot and about half were unsure if they could trust the advice given by a chatbot. Therefore, perceived trustworthiness, individual attitudes towards bots, and dislike for talking to computers are the main barriers to health chatbots.


title: Chatbot

text: In New Zealand, the chatbot SAM – short for Semantic Analysis Machine (made by Nick Gerritsen of Touchtech) – has been developed. It is designed to share its political thoughts, for example on topics such as climate change, healthcare and education, etc. It talks to people through Facebook Messenger.


title: Chatbot

text: In 2022, the chatbot "Leader Lars" or "Leder Lars" was nominated for The Synthetic Party to run in the Danish parliamentary election, and was built by the artist collective Computer Lars. Leader Lars differed from earlier virtual politicians by leading a political party and by not pretending to be an objective candidate. This chatbot engaged in critical discussions on politics with users from around the world.


title: Chatbot

text: In India, the state government has launched a chatbot for its Aaple Sarkar platform, which provides conversational access to information regarding public services managed.


title: Chatbot

text: "Hello Barbie" is an Internet-connected version of the doll that uses a chatbot provided by the company ToyTalk, which previously used the chatbot for a range of smartphone-based characters for children. These characters' behaviors are constrained by a set of rules that in effect emulate a particular character and produce a storyline.


title: Chatbot

text: The My Friend Cayla doll was marketed as a line of dolls which uses speech recognition technology in conjunction with an Android or iOS mobile app to recognize the child's speech and have a conversation. It, like the Hello Barbie doll, attracted controversy due to vulnerabilities with the doll's Bluetooth stack and its use of data collected from the child's speech.


title: Chatbot

text: IBM's Watson computer has been used as the basis for chatbot-based educational toys for companies such as "CogniToys" intended to interact with children for educational purposes.


title: Chatbot

text: Malicious chatbots are frequently used to fill chat rooms with spam and advertisements, by mimicking human behavior and conversations or to entice people into revealing personal information, such as bank account numbers. They were commonly found on Yahoo! Messenger, Windows Live Messenger, AOL Instant Messenger and other instant messaging protocols. There has also been a published report of a chatbot used in a fake personal ad on a dating service's website.


title: Chatbot

text: Tay, an AI chatbot that learns from previous interaction, caused major controversy due to it being targeted by internet trolls on Twitter. The bot was exploited, and after 16 hours began to send extremely offensive Tweets to users. This suggests that although the bot learned effectively from experience, adequate protection was not put in place to prevent misuse.


title: Chatbot

text: If a text-sending algorithm can pass itself off as a human instead of a chatbot, its message would be more credible. Therefore, human-seeming chatbots with well-crafted online identities could start scattering fake news that seems plausible, for instance making false claims during an election. With enough chatbots, it might be even possible to achieve artificial social proof.


title: Chatbot

text: The creation and implementation of chatbots is still a developing area, heavily related to artificial intelligence and machine learning, so the provided solutions, while possessing obvious advantages, have some important limitations in terms of functionalities and use cases. However, this is changing over time.


title: Chatbot

text: Chatbots are increasingly present in businesses and often are used to automate tasks that do not require skill-based talents. With customer service taking place via messaging apps as well as phone calls, there are growing numbers of use-cases where chatbot deployment gives organizations a clear return on investment. Call center workers may be particularly at risk from AI-driven chatbots.


title: Chatbot

text: Chatbot developers create, debug, and maintain applications that automate customer services or other communication processes. Their duties include reviewing and simplifying code when needed. They may also help companies implement bots in their operations.


title: Chatbot

text: A study by Forrester (June 2017) predicted that 25% of all jobs would be impacted by AI technologies by 2019.


title: Magi

text: Magi (; singular magus ; from Latin "magus", cf. ) were priests in Zoroastrianism and the earlier religions of the western Iranians. The earliest known use of the word "magi" is in the trilingual inscription written by Darius the Great, known as the Behistun Inscription. Old Persian texts, predating the Hellenistic period, refer to a magus as a Zurvanic, and presumably Zoroastrian, priest.


title: Magi

text: Pervasive throughout the Eastern Mediterranean and Western Asia until late antiquity and beyond, "mágos" (μάγος) was influenced by (and eventually displaced) Greek "goēs" (γόης), the older word for a practitioner of magic, to include astronomy/astrology, alchemy, and other forms of esoteric knowledge. This association was in turn the product of the Hellenistic fascination for Pseudo-Zoroaster, who was perceived by the Greeks to be the Chaldean founder of the Magi and inventor of both astrology and magic, a meaning that still survives in the modern-day words "magic" and "magician".


title: Magi

text: In the "Gospel of Matthew", "μάγοι" ("magoi") from the east do homage to Jesus, a child and the transliterated plural "magi" entered English from Latin in this context around 1200 (this particular use is also commonly rendered in English as "kings" and more often in recent times as "wise men"). The singular "magus" appears considerably later, when it was borrowed from Old French in the late 14th century with the meaning "magician".


title: Magi

text: Hereditary Zoroastrian priesthood has survived in India and Iran. They are termed Herbad, Mobad (Magupat, i.e. chief of the Maga), and Dastur depending on the rank.


title: Magi

text: The term only appears twice in Iranian texts from before the 5th century BCE, and only one of these can be dated with precision. This one instance occurs in the trilingual Behistun inscription of Darius the Great, and which can be dated to about 520 BCE. In this trilingual text, certain rebels have magian as an attribute; in the Old Persian portion as "maγu-" (generally assumed to be a loan word from Median). The meaning of the term in this context is uncertain.


title: Magi

text: The other instance appears in the texts of the Avesta, the sacred literature of Zoroastrianism. In this instance, which is in the Younger Avestan portion, the term appears in the hapax "moghu.tbiš", meaning "hostile to the "moghu"", where "moghu" does not (as was previously thought) mean "magus", but rather "a member of the tribe" or referred to a particular social class in the proto-Iranian language and then continued to do so in Avestan.


title: Magi

text: An unrelated term, but previously assumed to be related, appears in the older Gathic Avestan language texts. This word, adjectival "magavan" meaning "possessing "maga-"", was once the premise that Avestan "maga-" and Median (i.e. Old Persian) "magu-" were coeval (and also that both these were cognates of Vedic Sanskrit "magha-"). While "in the Gathas the word seems to mean both the teaching of Zoroaster and the community that accepted that teaching", and it seems that Avestan "maga-" is related to Sanskrit "magha-", "there is no reason to suppose that the western Iranian form "magu" (Magus) has exactly the same meaning" as well. But it "may be, however", that Avestan "moghu" (which is not the same as Avestan "maga-") "and Medean "magu" were the same word in origin, a common Iranian term for 'member of the tribe' having developed among the Medes the special sense of 'member of "the" (priestly) tribe', hence a priest."


title: Magi

text: Some examples of the use of magi in Persian poetry, are present in the poems of Hafez. There are two frequent terms used by him, first one is "Peer-e Moghan" (literally "the old man of the magi") and second one is "Deyr-e Moghan" (literally "the monastery of the magi").


title: Magi

text: The oldest surviving Greek reference to the magi – from Greek μάγος ("mágos", plural: "magoi") – might be from 6th century BCE Heraclitus (apud Clemens "Protrepticus" 2.22.2), who curses the magi for their "impious" rites and rituals. A description of the rituals that Heraclitus refers to has not survived, and there is nothing to suggest that Heraclitus was referring to foreigners.


title: Magi

text: Better preserved are the descriptions of the mid-5th century BCE Herodotus, who in his portrayal of the Iranian expatriates living in Asia Minor uses the term "magi" in two different senses. In the first sense ("Histories" 1.101), Herodotus speaks of the magi as one of the tribes/peoples ("ethnous") of the Medes. In another sense (1.132), Herodotus uses the term "magi" to generically refer to a "sacerdotal caste", but "whose ethnic origin is never again so much as mentioned." According to Robert Charles Zaehner, in other accounts, "we hear of Magi not only in Persia, Parthia, Bactria, Chorasmia, Aria, Media, and among the Sakas, but also in non-Iranian lands like Samaria, Ethiopia, and Egypt. Their influence was also widespread throughout Asia Minor. It is, therefore, quite likely that the sacerdotal caste of the Magi was distinct from the Median tribe of the same name."


title: Magi

text: As early as the 5th century BCE, Greek "magos" had spawned "mageia" and "" to describe the activity of a magus, that is, it was his or her art and practice. But almost from the outset the noun for the action and the noun for the actor parted company. Thereafter, "mageia" was used not for what actual magi did, but for something related to the word 'magic' in the modern sense, i.e. using supernatural means to achieve an effect in the natural world, or the appearance of achieving these effects through trickery or sleight of hand. The early Greek texts typically have the pejorative meaning, which in turn influenced the meaning of "magos" to denote a conjurer and a charlatan. Already in the mid-5th century BCE, Herodotus identifies the "magi" as interpreters of omens and dreams ("Histories" 7.19, 7.37, 1.107, 1.108, 1.120, 1.128).


title: Magi

text: Other Greek sources from before the Hellenistic period include the gentleman-soldier Xenophon, who had first-hand experience at the Persian Achaemenid court. In his early 4th century BCE "Cyropaedia", Xenophon depicts the magians as authorities for all religious matters (8.3.11), and imagines the magians to be responsible for the education of the emperor-to-be. Apuleius, a Numidian Platonist philosopher, describes magus to be considered as a "sage and philosopher-king" based on its Platonic notion.


title: Magi

text: Once the magi had been associated with "magic" – Greek "" – it was but a natural progression that the Greeks' image of Zoroaster would metamorphose into a magician too. The first century Pliny the Elder names "Zoroaster" as the inventor of magic ("Natural History" xxx.2.3), but a "principle of the division of labor appears to have spared Zoroaster most of the responsibility for introducing the dark arts to the Greek and Roman worlds. That dubious honor went to another fabulous magus, Ostanes, to whom most of the pseudepigraphic magical literature was attributed." For Pliny, this magic was a "monstrous craft" that gave the Greeks not only a "lust" ("aviditatem") for magic, but a downright "madness" ("rabiem") for it, and Pliny supposed that Greek philosophers – among them Pythagoras, Empedocles, Democritus, and Plato – traveled abroad to study it, and then returned to teach it (xxx.2.8–10).


title: Magi

text: "Zoroaster" – or rather what the Greeks supposed him to be – was for the Hellenists the figurehead of the 'magi', and the founder of that order (or what the Greeks considered to be an order). He was further projected as the author of a vast compendium of "Zoroastrian" pseudepigrapha, composed in the main to discredit the texts of rivals. "The Greeks considered the best wisdom to be exotic wisdom" and "what better and more convenient authority than the distant – temporally and geographically – Zoroaster?" The subject of these texts, the authenticity of which was rarely challenged, ranged from treatises on nature to ones on necromancy. But the bulk of these texts dealt with astronomical speculations and magical lore.


title: Magi

text: One factor for the association with astrology was Zoroaster's name, or rather, what the Greeks made of it. His name was identified at first with star-worshiping ("" "star sacrificer") and, with the "Zo-", even as the "living" star. Later, an even more elaborate mytho-etymology evolved: Zoroaster died by the living ("zo-") flux ("-ro-") of fire from the star ("-astr-") which he himself had invoked, and even that the stars killed him in revenge for having been restrained by him. The second, and "more serious" factor for the association with astrology was the notion that Zoroaster was a Chaldean. The alternate Greek name for Zoroaster was Zaratas / Zaradas / Zaratos ("cf." Agathias 2.23–5, Clement "Stromata" I.15), which – according to Bidez and Cumont – derived from a Semitic form of his name. The Suda's chapter on "astronomia" notes that the Babylonians learned their astrology from Zoroaster. Lucian of Samosata ("Mennipus" 6) decides to journey to Babylon "to ask one of the magi, Zoroaster's disciples and successors", for their opinion.


title: Magi

text: The word "mágos" (Greek) and its variants appear in both the Old and New Testaments. Ordinarily this word is translated "magician" or "sorcerer" in the sense of illusionist or fortune-teller, and this is how it is translated in all of its occurrences (e.g. Acts 13:6) except for the Gospel of Matthew, where, depending on translation, it is rendered "wise man" (KJV, RSV) or left untranslated as "Magi", typically with an explanatory note (NIV). However, early church fathers, such as St. Justin, Origen, St. Augustine and St. Jerome, did not make an exception for the Gospel, and translated the word in its ordinary sense, i.e. as "magician". The Gospel of Matthew states that magi visited the infant Jesus to do him homage shortly after his birth (). The gospel describes how magi from the east were notified of the birth of a king in Judaea by the appearance of his star. Upon their arrival in Jerusalem, they visited King Herod to determine the location of the king of the Jews's birthplace. Herod, disturbed, told them that he had not heard of the child, but informed them of a prophecy that the Messiah would be born in Bethlehem. He then asked the magi to inform him when they find the child so that he himself may also pay homage to the child. Guided by the Star of Bethlehem, the wise men found the child Jesus in a house. They paid homage to him, and presented him with "gifts of gold and of frankincense and of myrrh." (2.11) In a dream they are warned not to return to Herod, and therefore return to their homes by taking another route. Since its composition in the late 1st century, numerous apocryphal stories have embellished the gospel's account. implies that Herod learned from the wise men that up to two years had passed since the birth, which is why all male children two years or younger were slaughtered.


title: Magi

text: In addition to the more famous story of Simon Magus found in chapter 8, the "Book of Acts" () also describes another magus who acted as an advisor of Sergius Paulus, the Roman proconsul at Paphos on the island of Cyprus. He was a Jew named Bar-Jesus (son of Jesus), or alternatively Elymas. (Another Cypriot magus named Atomos is referenced by Josephus, working at the court of Felix at Caesarea.)


title: Magi

text: One of the non-canonical Christian sources, the Syriac Infancy Gospel, provides, in its third chapter, a story of the wise men of the East which is very similar to much of the story in Matthew. This account cites Zoradascht (Zoroaster) as the source of the prophecy that motivated the wise men to seek the infant Jesus.


title: Magi

text: In the Talmud, instances of dialogue between the Jewish sages and various magi are recorded. The Talmud depicts the Magi as sorcerers and in several descriptions, they are negatively described as obstructing Jewish religious practices. Several references include the sages criticizing practices performed by various magi. One instance is a description of the Zoroastrian priests exhuming corpses for their burial practices which directly interfered with the Jewish burial rites. Another instance is a sage forbidding learning from the magi.