The Daily Alaska empire., 1929-01-28
CEOPHONE FOR MINE RESCUE
 WORK IS HERE
Stewart Receives New h. strument as Addition to
 Mine Rescue Equipment

To the mine rescue equipment of the U. s. Bureau of Mines here was added last week geophone, listening device capable of de tecting sound through solid sub stance at varied distances ranging from 900 to 1.250 feet, according to B. D. Stewart, Mining Supervisor for Alaska It is mechanical instrument, sometimes called th earth stethoscope, and operates ol the same principles as the stetao scope, of the medical profession.
 It is a development of a war time invention that was used for the purpose of detecting enemy sapping and underground mining operations and for locating enemy artillery. It consists of two metal discs each of which is attached to ear-tubes.
 Detects Vibrations
 When placed in contact with the earth, MT Stewart said, either on the surface or underground, the geophone detects vibrations from a distance and through the rarefac- tion and compression of the air in the tightly sealed instrument these vibrations are transformed into sound waves and carried to the ears of the operator by means of rubber tubes. It is extremely sensitive, not only to vibration, but to the variations in the vibrations so that it is easy to detect the nature of the sound, whether it is pick, hammer, explosion, fire, run ming water or whatever the cause of the earth waves may be. An ex pertinent, it is said, was made by an engineer of the Bureau of Mines who never had used the instru- ment before: after listening to sounds caused by 12 different min ing and carpentering operations he was able with ease, correctly to name nine of them and accur- ately to describe the other three sounds although they were too un- familiar to him to allow him to name them. Talking and singing can be clearly heard through a 45-foot coal pillar and have been detected through 100 to 150 feet of coal
 Not Unlimited
 It is, however, not unlimited iT range. A pick striking into bitum inous coal is easily heard through 900 feet of intervening coal and earth, and sledge pounding can be heard 1,500 feet with sufficient clearness to enable the direction to be accurately noted The explo- sion of an ounce of dynamite transmits wave energy, translated as sound in the geophone, for more than 1000 feet.
 The instrument. MT. St wart said. is particularly valuable in locating the position of entombed miners. In practical use, 1t is placed on the earth in the vicinity where the accident has occurred At first the sounds will not be registered with the same force ir both ears of the listener. The disks are oriented until the volume is the same in each ear. The point of origin is then at right angles tC the operator. The same operation is repeated from a different angle and where the two lines intersec is the point from which the sound originates.
 Many Uses
 The geophone has a number o other uses. It aids in preventing accidents; in metal mining experi ence has shown it can be used t, bring the ends of two borings to gether, eliminating costly surveys it locates with surprising accurac. leaks in water mains, knocks Il automobile valves and cylinder and has other uses.
 The instrument will be kept her in MT. Stewards office and will b available for use as needed b mine operators or others, he said
 ATTENTION MOOSE