bluuebunny/crossref_metadata_2025 huggingface dataset:
MEASUREMENTS OF TEMPERATURE COEFFICIENT AND PRESSURE COEFFICIENT OF QUARTZ CRYSTAL OSCILLATORS
Authors: Brown S. Leroy , Harris Sidon
Published: February 2005

A method of measurement is used whereby variation in frequency of a high frequency oscillator can be measured easily to a fraction of a part in a million. The audible difference tone produced by a harmonic of a constant, high frequency oscillator and a harmonic of a second oscillator is compared to the tone of a variable, calibrated audio frequency oscillator. Any change of the frequency of the second high frequency oscillator is measured to a fraction of a cycle per second. This method of measurement is used to determine the effects of temperature and pressure on the frequency of a piezo-electric oscillator. The temperature effect is of the order of 20 parts per million per degree centigrade while the pressure effect is of the order of only 6 parts per million per atmosphere.
MEASUREMENT OF FIBER DIAMETERS BY THE DIFFRACTION METHOD
Authors: McNicholas H. J. , Curtis H. J.
Published: February 2005

The classification of wool fibers into standard grades is based entirely on the average diameter of the fibers. The diffraction of light by a bundle of parallel fibers was employed by Thomas Young in 1824 in a simple ingenious instrument for the rapid direct measurement of average diameter, but no thorough investigation has ever been made of the practical possibilities of this method in the routine grading of wool.

In the present paper a new construction of Young's instrument (the eriometer) is described, and a critical study is made of the accuracy and adaptibility of the instrument in the averaging of a wide range of diameters as distributed in a group of fibers. Sources of error and limitations of the method are discussed.

It is found that the eriometer average is in excellent agreement with comparable data obtained with the microscope. The method affords considerable opportunity for the further development of instruments to include additional features desirable in the study of wool or other textile fibers.
A SPECTROGRAPH PLATE SHIELD
Authors: Lay J. Tracy , Cornog I. Clyde
Published: February 2005

A shield designed for use in a spectrograph to prevent pre-exposure and subsequent exposure of the photographic plate due to scattered light when a number of spectra are photographed on the same plate or film. The use of such a shield eliminates consequent errors in the densities of spectral lines as determined by a densitometer.
AN AUTOMATIC RACE TIMER
Authors: Speakman Edwin A.
Published: February 2005

The instrument described is used to time races by the use of a microphone, a photoelectric cell, an amplifier, and a clock. The time is recorded in 1/120 of a second from the instant when the sound of the starting gun reaches the runner's ear to the instant when the runner's chest touches the tape at the finish.
A CONCAVE ULTRASONIC DIFFRACTION GRATING
Authors: Thompson George E.
Published: February 2005

A concave ultrasonic diffraction grating and mounting have been used to measure ultrasonic wave lengths between one and three milliameters. An oscillating quartz crystal serves as generator and receiver of the waves. The results are compared with those obtained by the Pierce interferometer and found to agree quite well.
A PRECISION X-RAY SPECTROMETER AND THE WAVE LENGTH OF Mo Kα1
Authors: Compton Arthur H.
Published: February 2005

An x-ray spectrometer was designed with the first crystal mounted on an arm supported by the frame of the spectrometer, and with the second crystal mounted on the central table of the instrument, whose position is read from a precision circle. The ionization chamber (of 28 cc capacity, filled with krypton) is on an arm whose position is read by a second precision circle. The instrument was built by the Societe Genevoise de Physique.

The first crystal was adjusted to throw the Kα1 line of molybdenum over the main axis of the spectrometer, and measurements were made with the second crystal in the (1, −1), (1, +1), (1, −4) and (1, +4) positions (Allison's notation). The reflection maxima from calcite (corrected to 18° C) occur at θ1=6°42′35.″5 and θ4=27°51′33.″0 with a probable error of 0.″25 due chiefly to errors in reading the circle. Using an apparent grating space for the first order of 3.02904A at 18° C, we get λ=707.830±.002 mA. Larsson obtained 707.831±.003 mA using Siegbahn's photographic method. Comparison of θ1 and θ4 gives for the index of refraction in calcite, 1 −μ=(2.10±.15)×10−6, as compared with Hatley's value of (2.04±.09)×10−6.
THE USE OF THE WILSON CLOUD CHAMBER FOR MEASURING THE RANGE OF ALPHA-PARTICLES FROM WEAK SOURCES
Authors: Kurie F. N. D.
Published: February 2005

A large Wilson cloud chamber operated by a synchronizing mechanism similar to that used by Blackett is described. It is shown how, by the use of mirrors, it is possible to take two photographs of the whole volume of the cloud chamber with a single lens, which are equivalent to photographs taken by two cameras at right angles. The design of such a camera is discussed in detail. The photographs are examined by replacing the developed film in the camera and using it as a projection apparatus. The two images can be combined on a suitably oriented plate as one image the same size as the original track. The method is thoroughly tested by photographing glass fibers and by range determinations. The reduction of the track lengths in the chamber to α-particle ranges under standard conditions is discussed fully. It is shown that the interval between expansions must be made much longer than is customary if precision is to be attained in this reduction. The temperature in the chamber is carefully examined throughout the single cycle and repeated cycles to determine this interval and other thermal conditions of operation. The whole technique has been developed with the aim of utilizing as many tracks per expansion as possible for the purposes of range measurement.
THE JOULE MAGNETOSTRICTIVE EFFECT IN A GROUP OF COBALT-IRON ALLOYS
Authors: Williams S. R.
Published: February 2005

In the course of studying various ferromagnetic rods, a group was found which showed a wide variation in the type and magnitude of the changes in length which occur when they were magnetized longitudinally. This collection included rods of iron, nickel, cobalt and alloys of cobalt-iron. In a later paper it is proposed to correlate the final results in this paper with the mechanical hardness, elastic properties, hysteresis loss and change in resistance due to a magnetic field. In making the following study a new extensometer and recording camera were used. These are described in the following pages.
A FILTER FOR AN X-RAY POWER SUPPLY
Authors: Hoag J. Barton , Andrew Victor J.
Published: February 2005

A combination of a Greinacher rectifier circuit and balanced pi-type low-pass filter is described which supplies an x-ray tube 30 milliamperes at 20 kilovolts with a ripple of less than 0.02 percent.
A NOVEL OPTICAL SCREEN FOR CLASSROOM DEMONSTRATIONS
Authors: Howey Joseph H.
Published: February 2005

A new optical screen has been designed for making rays of light visible to large lecture classes. The rays are made to strike obliquely across the screen, making a small angle with the plane of the screen. The behavior of rays of light incident on mirrors, lenses, and prisms can be conveniently demonstrated by using the ordinary forms of these optical devices without any special mountings. On account of the efficient utilization of the available light, this screen makes possible a large size pattern of the paths of the rays so that the pattern can be observed from all parts of a large lecture room. The rays of light are in full view of both the demonstrator and the class at all times.
APPARATUS FOR SPECTROSCOPIC STUDIES IN THE INTERMEDIATE INFRARED REGION—20 TO 40μ
Authors: Strong John
Published: February 2005

An infrared spectrometer is described which has the following features: (1) The entire optical path may be evacuated to about 10−4 mm of mercury pressure by the use of charcoal cooled with liquid air. (2) Exit and entrance slits are both adjusted from outside the vacuum by a single graduated head. (3) The optical system is arranged to use one mirror for telescope and collimation with the slits arranged on its optical axis. (4) The prism (or grating) is rotated by a 10-inch lever actuated by an ordinary micrometer. This lever connecting the prism table, which is in vacuum, with the micrometer which is outside, is sealed by a sylphon tube. (5) By connecting the micrometer head mechanically to a recording galvanometer the spectrometer may be made self-recording. (6) The spectrometer is constructed in such a way as to give the thermopile maximum isolation from thermal fluctuations in the room.

An absorption cell is described which has the following features: (1) The cell has small windows although it will handle a beam having a numerical aperture of ⅓. (2) The radiation path in the absorbing gas is one meter. The cell may be evacuated or it will withstand pressures of several atmospheres. (4) The cell may be heated to 300°C.

Various techniques for obtaining monochromatic bands of infrared radiation are discussed. A technique is described which makes spectroscopic measurements possible with a source whose temperature may fluctuate (such as the crater of a carbon arc).
THE WENNER POTENTIOMETER
Authors: Behr Leo
Published: February 2005

A two-range, five-dial potentiometer is described which incorporates a decade construction suggested by Wenner. The upper range is 1.9111 volts in steps of 10 microvolts and the lower range is one tenth of this. The effect of contact resistance, thermal emf's and of errors in adjustment is considered in detail.

The limit of error for the instrument is 0.005 percent or 2 microvolts for the high range and 0.01 percent or 0.2 microvolt for the low range.
A PERIODIC RADIOMETER FOR ELIMINATING DRIFTS
Authors: Firestone F. A.
Published: February 2005

It is shown that while the Pfund resonance radiometer reduces the effect of drifts by a factor of several hundred, its advantage over the conventional Moll amplifying system as regards the reduction of the effect of Brownian motion on the accuracy of the readings is only about a factor of three for a resonance radiometer system requiring 140 seconds for a single observation. For a Moll system and a resonant system of equal times of observation, the Moll system is about twice as good as regards Brownian error in the readings. A resonance radiometer loses both its Brownian advantage and its ability to reduce drifts, when designed for a short time of response.

A periodic radiometer particularly suitable for rapid recording is described, drifts being completely eliminated, while the time of response is only six seconds. Two condensers in series with the amplifying circuit effectually stop all drifts while passing the periodic deflections. By averaging visually a considerable number of deflections, the accuracy of the resonance radiometer for equal reading time can be approached so that the same instrument may serve both for rapid exploration of spectra and more careful determination of detail.

Infrared spectra of high resolution have been successfully recorded from a grating spectrometer and in amount of detail shown, closely approach the most carefully manually recorded curves.
THE DESIGN OF TEMPERATURE CONTROL APPARATUS FOR PIEZO OSCILLATORS
Authors: Andrew Victor J.
Published: February 2005

The procedure is described for calculating the dimensions of the different components of a temperature control system consisting of conducting and insulating layers outside the thermostat, and absorbing, and in some cases insulating layers between the thermostat compartment and the quartz plate mounting.

A method is explained for observing and empirically reducing the effect of variations of room temperature on the controlled temperature of the apparatus. This effect depends on the relative positions of the thermostat, the heater, and the quartz plate. It is usually the limiting factor in precision of control.
A FIELD INTENSITY METER
Authors: Brown G. H. , Koehler Glenn
Published: February 2005

The fundamentals of field intensity measurements are summarized. The general methods of using a receiving set and a source of voltage for calibrating are outlined. The methods are then extended in application to a radio receiver which utilizes a modified superheterodyne circuit. The resultant beat note is of low frequency, and may be greatly amplified by means of audiofrequency stages of amplification. This gives the receiver not only extreme sensitivity but also great selectivity.

In other methods of measurement, the apparent field strength depends on the amount of modulation of the incoming wave. In the method here described, the beat note with the carrier wave is so great, compared to any contribution of the side-bands, that the meter readings do not change by any noticeable amount when a transmitting station ceases to modulate and transmits only the carrier wave. The beat note with the carrier wave is so great that it is possible to make measurements on stations whose fields are so weak that they cannot be detected on an ordinary receiver.

The attenuator is of the capacity type with a range of voltage from less than 1 microvolt to 3×106 microvolts. Detailed descriptions of the receiver and attenuator are given, as well as the methods of calibrating the apparatus.
A SIMPLE MANOMETER UTILIZING A NONVOLATILE LIQUID OF LOW DENSITY
Authors: Malmberg C. G. , Nicholas Warren W.
Published: February 2005

Closed end manometers utilizing organic liquids instead of mercury have the disadvantage that gas dissolves in the liquid and eventually accumulates in the closed end. A manometer is described with which the removal of gas from the liquid and from the closed end is quickly and effectively accomplished.
A Sensitive Differential Manometer
Authors: Hurst William
Published: February 2005

A portable sensitive differential manometer is described. The instrument consists essentially of a train of gears from a small jeweled wrist watch movement and a drum covered with a rubber diaphragm. The design is such as to permit the measurement of rapid and slight variations of pressure. The pressure variations may be as small as 0.0012 cm of mercury and as rapid as 15 per second. The above sensitivity may be increased by a factor of approximately 10 by increasing the effective volume behind the moving diaphragm.
A Wide-Range Beat-Frequency Oscillator
Authors: Hall A. C.
Published: February 2005

A beat-frequency oscillator is described which has a frequency range from 5 kilocycles to 1600 kilocycles, and a maximum power output of ten watts. Broad-band amplifier principles are utilized in the design to obtain an output voltage substantially independent of frequency throughout the range of the oscillator.
A Negative-Feedback Linear-Pulse Amplifier
Authors: Waddel Ramond C.
Published: February 2005

A linear pulse amplifier is described which utilizes the principle of negative feedback. The amplifier is substantially unaffected by changes in supply voltages and provides either positive or negative output pulses with practically exact linearity and little backwave. The circuit components are easily obtainable and of moderate cost. A mechanical design is suggested which minimizes the labor of construction.
Exhaust Valve for Pneumatic Cloud Chambers
Authors: Fussell Lewis
Published: February 2005

An air valve designed for the purpose of triggering the expansion of a pneumatic cloud chamber utilizes Bridgman's ``unsupported area'' seal. The valve is controlled by a magnet constructed from the field coil of an inexpensive dynamic loudspeaker. This design allows vacuum tube control of forces up to 75 pounds. High speed of operation (∼1/300 second) recommends its use with counter control, and its extreme simplicity is advantageous in general work.
Cloud Chamber Control Circuit
Authors: Getting I. A.
Published: February 2005

A simple circuit employing neon-filled cold cathode thyratrons is described for use in controlling cloud chambers. The circuit operates on the standard d.c. line and performs reproducible cycles with great precision and extreme ease of adjustment of time intervals between successive steps of the cycle.
A Direct-Reading Counting Rate Ratio Meter
Authors: Evans Robley D. , Meagher Ralph E.
Published: February 2005

We describe a multi-staged thermionic amplifier, using two discharge counters, and having an output meter which reads directly the ratio of the activity of two radioactive sources. Continuous photographic recording of this ratio for two fractions of a rapidly decaying source therefore provides a direct observation of their relative activity which is invariant with time, even though a mixture of substances having a variety of half-periods is involved. The amplifier holds advantages of greater convenience and higher statistical accuracy over the usual single counter amplifier when dealing with sources having moderate strength and half-periods near the range of five minutes to one hour. It is particularly suited to experiments in which such radioactive substances are used as chemical or biological indicators. A portion of the circuit, consisting of three thermionic tubes, has general applicability wherever direct observations are wanted of the ratio of two d.c. currents.
The Design of Powerful Electromagnets Part IV. The New Magnet Laboratory at M. I. T.
Authors: Bitter F.
Published: February 2005

This paper deals with the details of design and operation of air core water-cooled coils dissipating up to 1700 kilowatts. Four magnets have been built and used. The first is intended primarily for the measurement of the magnetization of any substance at any temperature in fields up to 40,000 gauss. The second was designed to test the desirability of a new type of construction. The third gives fields up to 100,000 gauss uniform within 1 percent in a volume of 25 cc, and is to be used primarily for Zeeman effect and other optical experiments. The fourth can produce fields up to 50,000 gauss uniform within 1 percent in a volume of almost a liter, and is designed primarily for experiments at very low temperatures. The power to operate these magnets is supplied by a motor generator capable of giving 10,000 amperes at 170 volts continuously.
Two Voltage Regulators
Authors: Neher H. Victor , Pickering William H.
Published: February 2005

Two voltage regulators are described. The first is satisfactory where there is only a very small current drain; the second will maintain constant voltage output up to the current carrying capacity of the radio tube. For each the change of output voltage with change of input can be made zero. Where extreme constancy is required, the second circuit described is recommended. It approximates closely perfect regulation. The coefficient of voltage change of the output, defined by (1/V0)(∂V0/∂Vi) where V0 is the output voltage and Vi is the input voltage, is less than 10−7 per volt. The regulation is equally as good for surges as for longer random or periodic fluctuations. The circuit also maintains a constant voltage output for varying current drains, the output resistance being about 10 ohms. Currents up to 100 milliamperes at several thousand volts may be drawn with no significant change in the output voltage. The coefficient of drift defined by (1/V0)(∂V0/∂t), where t is the time, will usually be less than 10−4 per hour even under normal laboratory conditions where no special precautions are taken.
A Practical Negative Resistance Oscillator
Authors: Brunetti Cledo
Published: February 2005

A simple, all-purpose oscillator of the negative resistance type called the ``transitron'' oscillator is described. The simplicity of the circuit is such that with the data included herein one may construct the oscillator in a minimum of time and with little effort. Possessing exceptionally good wave form with the attendant efficiency in keeping its frequency from drifting once a definite frequency of oscillation is selected, the oscillator should find favor in general physics laboratories. The versatility of the device lends itself to application in many types of physical research, some of which are described, as well as to the construction of standard physics laboratory apparatus requiring an oscillator as a component part. Use of the oscillator is recommended in medical, biological, psychological, and other fields of research where a source of low voltage at variable frequency is often desired and where the simplicity of the device should be of great help.
A Null Detector for A.C. Bridge Measurements
Authors: Binns J. E. , Webb Harold W.
Published: February 2005

A new type of bridge detector is described which has almost constant sensitivity in the frequency range 25 cycles to 70,000 cycles, and which is simple to operate, rugged, and stable.
A Portable High Voltage Supply
Authors: Huntoon R. D.
Published: February 2005

A portable power supply capable of furnishing up to 2500 volts at ten microamperes is described. An input of 45 volts at 3 milliamperes gives 600 volts output with a constancy equal that of the driving battery. The weight including the 600-volt output condenser but excluding batteries is 450 grams. A modification requiring a 90-volt supply and weighing 175 grams is discussed. Possible additional uses such as pulse generator, counting-rate-meter and ignitron control are mentioned.
Viewing Tubes for High Pressure
Authors: Roebuck J. R. , Miller E. E.
Published: February 2005

An oversize tube of transparent plastic is put into a slotted steel supporting tube by cooling in liquid air. Such a device using Bakelite BT 43 001 has proven reliable at 400 atmospheres, and calculations indicate 1000 atmospheres as the upper limit of safety for tubes of this general type and material. The most important feature is the absolute reliability. This is due to the fact that in operation no primary tensile stresses exist in the transparent material.
An Investigation of the Linear Accelerator
Authors: Hartman Paul L. , Smith Lloyd P.
Published: February 2005

A treatment of the acceleration of particles by the linear resonance accelerator is given, including the calculation of the velocity distribution of particles emergent from the device and a method for improving the yield and the velocity distribution. Calculated curves showing these features are shown. The mass selection properties of the device are also considered. Focusing is considered briefly and a discussion of the characteristics of a quarter wave-length line as applied to a resonance accelerator is included. The experimental features of a linear accelerator as built up are described. Probable particle energies to be expected from any future device of the kind are indicated.
A Study of the Rideal Absorption Hygrometer
Authors: Harkness H. W.
Published: February 2005

The Rideal absorption hygrometer has been studied with a view to its possibilities as a laboratory instrument for the measurement of the hygroscopic condition of gas in small and confined spaces. The theoretical errors due to adsorption of moisture upon the containing walls of the apparatus, and the error introduced by the presence of stagnant air in the connecting tubes of the hygrometer, have been derived. The nature of the theoretical error due to adsorption is supported by experiments. The temperature changes occurring in the hygrometer, during the process of an experiment, have been followed and corrections applied. The results, thus corrected, show reasonable agreement with the published data upon the saturated vapor pressure of water. Finally a hygrometer has been built suitable for immersion in a thermostat. Measurements with this instrument have been compared with reliable dew point determinations taken in a hygrostat of special design.
A New Form of Expansion Liquefier for Helium
Authors: Cooke A. H. , Rollin B. V. , Simon F.
Published: February 2005

A short description is given of an expansion liquefier which yields a supply of liquid helium in a Dewar vessel and is very economical in liquid hydrogen.
On Methods for Measuring and for Automatically Regulating the Speed of the Ultracentrifuge
Authors: Björnståhl Yngve
Published: February 2005

In the first part an account is given of the methods, tried in the Laboratory of Physical Chemistry, Upsala, for measuring the speed of the ultracentrifuge. The methods can be classified according to the nature of the primary indicator, which may be of optical or of electrical design. In the first case (optical methods) the stroboscope and a photo-cell device are considered. In the second case an electrical indicator of the following type has been designed and constructed. A part of the rotor shaft has been magnetized in a radial direction and a stator is mounted in the centrifuge casing. The frequency or the e.m.f. of the power produced by the indicating generator is measured by means of different methods. The oscillograph, different resonance circuits and bridge circuits have been considered. In the second part a description is given of a device for the automatic regulation of the speed of the ultracentrifuge. The frequency from the indicating generator is connected to a bridge. The output voltage from this is applied to a phase reversing bridge, which controls the oil supply to the centrifuge turbines by means of relays.
Sensitivity and Resolution of Moving Coil Galvanometers. I
Authors: Cartwright C. Hawley
Published: February 2005

The volt and ampere sensitivity of a moving coil galvanometer is treated in terms of the electrical circuit, the galvanometer design, and the time used for taking observation. Only cases where the current is constant are discussed; ballistic use is not treated. The term ``resolution of galvanometer readings'' is suggested to describe the experimentally determined change in potential difference or current that can be measured with a stated probable error in a stated measuring time under actual working conditions. The use of a galvanometer as a deflecting, partial-deflecting and null instrument is discussed.
A Constant Path Acoustic Interferometer for Gases at Variable Pressure
Authors: Herget Carl M.
Published: February 2005

A constant path acoustic interferometer is described, which operates by varying the pressure of the gas being studied. This variation in pressure results in the appearance of standing waves between the crystal and reflector. The resulting reaction peaks, detected by the usual methods, allow of determination of the wave-length, and consequently the velocity, if the frequency be known. Comparison is made of the results on ethylene gas at 23.0°C and pressures between 35 to 55 atmospheres obtained with this instrument and those of a moving reflector interferometer. The two sets of data agree within the limits of error of the measurements.
A Comparison of the Use of Crystal-Reflected and Filtered X-Rays in Liquid Diffraction Patterns
Authors: Gregg R. Q. , Gingrich N. S.
Published: February 2005

X-ray diffraction patterns of liquid sodium have been obtained under different conditions of monochromatization, collimation, and tube voltage. It is shown that of the methods tried, monochromatization by rocksalt crystal reflection is the most desirable and the most expedient method. Furthermore, an entirely spurious peak can be introduced into the pattern under certain conditions when filtered x-rays are used.
Correction Table for the Effect of Coriolis Acceleration on Bubble Sextant Altitudes
Authors: Stewart John Q.
Published: February 2005

At modern speeds of aeroplane flight the Coriolis force, to which any moving body is subject on the rotating earth, produces a sensible displacement of the horizon as found by gravity. This note presents the necessary correction formulae and tables for astronomical altitudes taken in flight with the bubble sextant. This correction usually exceeds the atmospheric refraction, and in precise celestial ``avigation'' its application should become standard routine.
Transmission and Reflection of Plastics and Metal Blacks in the Far Infra-Red
Authors: Seifert H. S. , Randall H. M.
Published: February 2005

Transmissions and reflections have been measured at nine wave-lengths between 20.7μ and 152μ for a number of plastics and special surfaces. The residual rays from crystals were used as sources of approximately monochromatic radiation. The general purpose of the investigation is to find materials for absorbing and transmitting filters to be used in the far infra-red region of the spectrum. The spectroscopy of the far infra-red depends primarily upon the use of absorbing filters and reflecting surfaces to obtain purity of spectra. Relatively few materials are suitable for these purposes and additional materials are greatly needed. Vacuum spectrographs and absorption cells require transparent windows capable of standing pressure. It is difficult to avoid using less than four such windows in any spectroscopic arrangement. If the transmission of the individual windows can be raised from 60 percent to 80 percent the transmission of the four is increased by a factor of more than three. Similarly it is a matter of importance that the absorbing material on the receiving surfaces of the thermopile be efficient in transforming incident radiant energy into heat. The satisfactory solution of these technical requirements in the far infra-red is a much more difficult one than in the near infra-red, with the result that extended investigations to discover materials suitable for these various purposes cannot well be avoided. The results recorded here deal primarily with plastics though a number of other substances are included.
A New Design of a Heat Exchanger for Liquefiers
Authors: Goetz Alexander
Published: February 2005

A new design of a Linde type exchanger for a medium sized air liquefier is described, characterized by a simple and efficient spatial distribution of the high pressure tubes in the low pressure system, using for the latter rubber hose reinforced with canvas. The performance data of the exchanger are given.
The Electrically Driven Magnetically Supported Vacuum Type Ultracentrifuge
Authors: Skarstrom C. , Beams J. W.
Published: February 2005

The electrical motor drive and the magnetic support for the vacuum type ultracentrifuge have been revised and improved. The drive is a two-phase motor and the support a solenoid which attracts a solid steel cylinder fastened to the rotating parts. The armature of the motor consists of a solid steel cylinder and a magnetic core support mounted coaxially on a stainless steel tubular shaft. Cooling water passes through the tubular shaft. A two-phase salient pole stator produces the rotating magnetic field when actuated by the output of a transitron oscillator and power amplifier. Condensers in series with the motor field windings split the phase and match the load to the power amplifier. At an oscillator frequency of 1188 cycles per second and an input to the motor of 1 kw, the rotating magnetic field produces a torque of 600 g-cm throughout the starting period up to about 10 percent slip (about ½ hp at 1000 r.p.s.). A 7½-lb rotor (6¼″ diameter, moment of inertia of 81,000 g-cm2) has been accelerated to 1000 r.p.s. in about 18 min. Upon reaching the desired operating speed, a slip speed control actuated by a magnetic pick-up on the centrifuge shaft sharply reduces the power input to the motor and automatically holds the rotational speed constant to within 0.05 percent. When the slip is not too large, the mechanism provides a satisfactory ultracentrifuge drive which is ``run-away proof'' and which automatically maintains its speed within ½ r.p.s. from day to day.
Calibration of Neher-Harper Counter Circuit for Accurate Comparison of β- or γ-Ray Sources
Authors: Hull D. E.
Published: February 2005

The conditions affecting the reproducibility of a thin-walled all-glass type counter used with the Neher-Harper quenching circuit have been investigated. The plate voltage and grid bias on the quenching tube are the most critical factors, and experimental arrangements for holding them constant are described. An upward drift in counting rate is noted at rates of the order of 100 per sec., and methods for minimizing the effect of this drift on the accuracy of the measurements are described. A new method of calibrating a counter circuit is used. The activity of a sample of radon is measured under the same geometrical conditions at different times, and by use of the accurately known half-life of radon, the counting losses at various speeds are determined. A variation of the multiple-addition method of calibration is also used with concordant results. It is found that with proper precautions the counter can be used to measure counting rates in the range from 30 to 200 per sec. with an accuracy of 0.2 to 0.3 percent.
An A.C. Operated D.C. Amplifier with Large Current Output
Authors: Treviño S. N. , Offner Franklin
Published: February 2005

The theory and design of an a.c. operated d.c. amplifier with large current output are presented. A d.c. phase inverter using cathode in-phase degeneration drives the push-pull output stage. The output is linear over a range of 160 ma.
The Production of Annular Magnetic Fields of Great Uniformity
Authors: Ference Michael , Shaw A. E. , Stephenson R. J.
Published: February 2005

In the magnetic focusing of electron or ion beams, it is important to secure magnetic fields which possess homogeneity over the region in space traversed by the beam. Helmholtz coils, frequently used for this purpose, provide the desired uniformity of field only for a limited region coaxial with the coils, but for regions off the axis in the median plane, the magnetic field is not uniform. It has been shown theoretically and verified experimentally that in order to obtain the necessary uniformity off the axis in the median plane, the axial separation of the coils must be diminished; this separation depends upon the region in which the uniformity is desired. A pair of coils whose separation may be varied has been constructed of mean radius 30.712 cm, each having 900 turns and an approximate square cross section of windings of side 6.856 cm. The field due to the coils has been explored off the axis in the median plane using a standard coil and magnetometer. The measurements reveal that the uniformity produced with the new separation is vastly superior to that which results from the usual Helmholtz separation.
The Use of Electrets in Electrical Instruments
Authors: Gemant Andrew
Published: February 2005

An electret is a permanently electrically polarized material and exhibits an electric field near its free surface which keeps undiminished for years. It is possible to utilize this field in electrical appliances. Experiments and devices on this line are described in the following paper.
A Design for an Electromagnet and Performance of a Small Model
Authors: Freed Simon
Published: February 2005

The windings of the magnet are made of continuous lengths of copper tubing with cross section shown in Fig. 1. Water at high pressure is sent through the hollow center for cooling. The conductor is wound about the core in such a way that the resistance to the flow of the water is reduced to about half what would prevail in a magnet of conventional design. These features make possible a high effective current density. The disposition of the coils and the shape of the iron core were based on the experiences with the big magnets in Upsala and in Paris. A model gave the results indicated in Fig. 5. When the pole faces 2.5 cm in diameter were separated by 7 mm the field obtained was 33,200 gauss using 16 kw. The model was constructed to employ water at considerably higher pressures than were actually tried. A higher current density would then be permitted without risk of serious electrolytic corrosion.
A Method and Instrument for the Measurement of Very Small Amounts of Heat and Very Small Changes of Temperature
Authors: Zamenhof S.
Published: February 2005

A thermometer is described which detects temperature changes of the order of 10−4 °C and quantities of heat of the order of 10−4g cal. It is essentially a gas or vapor thermometer in which the shift of the top of the meniscus of an indicating liquid is observed through a microscope. The shift is due to changes of the shape of the meniscus while the circumference remains stationary. Hence the sensitivity depends upon the surface tension of the indicating liquid but not on the friction between the liquid and the glass.
The Application of the Method of Coincidence Counting to Experiments in Nuclear Physics
Authors: Dunworth J. V.
Published: February 2005

The paper describes the principles involved in the application of coincidence counting to problems in nuclear physics, and gives details of the various methods of approach to the solution of nuclear level schemes, with some of the difficulties encountered. It is shown that the maximum source strength which can be used is inversely proportional to the coincidence resolving time and that the method of experiment has the great advantage over most other methods in that it can be used with very weak sources (sources having an activity of about 10−5 millicurie). An accurate knowledge of the absolute net efficiency of a Geiger counter for all types of radiation is required in the interpretation of the coincidence rates, and the method of achieving this at the same time as information is obtained about nuclear level schemes is explained. Further, it is pointed out that the method makes possible a simple and rapid determination of the total energy of disintegration of β-radioactive nuclei and therefore of the mass differences between parent and daughter nuclei.
A Condenser Type High Speed Engine Indicator
Authors: Roess Louis C.
Published: February 2005

The condenser type of pressure pick-up for a high speed engine indicator has advantages of simplicity, ruggedness, and frequency response over other types. As used ordinarily, with a d.c. polarizing voltage, fidelity at low frequencies requires the use of a very high impedance input circuit, with consequent troubles from poor stability, low sensitivity, and particularly ignition pick-up. The latter has required the use of airplane type shielding on ignition systems. These difficulties have been completely overcome by use of a high frequency (several megacycles per second) ``polarizing voltage'' in conjunction with a special bridged T type of balancing circuit. The T elements of this circuit can be built into the pick-up very simply and ruggedly, thereby eliminating difficulties with capacity changes in the lead wires. The sensitivity of the circuit is such that very little amplification is required. Frequency response is limited only by the elastic characteristics of the diaphragm. Both pressure-time and rate of pressure change-time cards can be observed and photographed. The wide frequency response of the indicator makes it particularly applicable to the study of knocking combustion.
Some Improvements in a Geiger-Müller Counting System
Authors: McMaster Harold , Pool M. L.
Published: February 2005

A new method of interpolation is described which eliminates one tube per scale-of-two and does not disturb the equilibrium of the trigger tubes. A resolving time of 10−4 second was obtained with a quenching circuit incorporating the desirable features of both the Neher-Harper and the multivibrator circuits.
A Mass Spectrometer for Routine Isotope Abundance Measurements
Authors: Nier Alfred O.
Published: February 2005

A mass spectrometer suitable for routine isotope analyses of carbon, nitrogen, and other light elements which may be put in the gaseous or vapor form is described. Although a simple, relatively inexpensive magnet consuming little power is used, good resolution is obtained.
Work's Method for Balancing the Kelvin Double Bridge
Authors: Patterson G. R.
Published: February 2005

The Kelvin double bridge for measuring low resistances usually is balanced by either variable ratio arms or by a variable standard resistor. For the calibration of fixed value standard resistors when the major ratio arms and the bridge standard are fixed value precision standards, Work's method obtains the balance of the bridge by passing an adjustable auxiliary current through the standard.
Photo-Cell Multiplier Tubes
Authors: Larson C. C. , Salinger H.
Published: February 2005

Structural and performance data on a Cs–Cs2O–Ag type of photoelectric cell whose current output is amplified by an integral 6- or 11-stage electron multiplier are given.
A Balanced Direct-Current Amplifier for Alternating-Current Operation
Authors: Stair R. , Hand I. F.
Published: February 2005

This paper gives technical data on a Wheatstone bridge type of balanced direct current photoelectric amplifier adapted for use on 110-volt a.c. commercial power lines. The instrument is especially designed for use with the standard recorders employed by the U. S. Weather Bureau, and is to be used in the study of ultraviolet solar radiation and the determintaion of the amount and variation of ozone in the stratosphere. Performance tests indicate that the instrument is equivalent to the older battery type in sensitivity and precision. It is, furthermore, free from the disadvantages of requiring constant voltage adjustments, sensitivity tests, and the constant attention of an experienced operator.
A Focal Isolation Monochromator for the Schumann Region
Authors: Duncan A. B. F.
Published: February 2005

A fluorite vacuum monochromator and auxiliary apparatus for the study of photochemical reactions in the region 1300–1900A are described. Lines in the nitrogen arc spectrum were isolated in as high as 85 percent purity. Estimates from three sources give intensities of the order of 1×1013 quanta per second for the 1742–45A doublet.
A Continuously Variable Oscillator for Parallel Line Measurements at 100 to 1000 Megacycles
Authors: King Ronold
Published: February 2005

The theory discussed in earlier papers regarding the essential characteristics of generators for parallel line measurements at ultra-high frequencies has been applied to design a simple circuit for oscillators using tubes, such as the 1020Y, in which the electrodes are themselves open-end sections of a parallel line. The new circuit permits coupling to a Lecher system in a manner which is geometrically both short and close, but electrically loose. The frequency of the oscillator described is continuously variable from 100 to 1000 megacycles.
A Multiple Sweep System for Cathode-Ray Oscillography
Authors: Talbot Samuel A.
Published: February 2005

The usefulness, efficiency and economy of cathode-ray oscillography are improved by sweeping the spot across several successive lines on the face of the tube. There is presented a circuit which does this, with flexibility as to speed, delay, spacing and brightness of the individual traces. A modified sweep circuit actuates a trigger unit which shifts each trace and brightens it during the transit.
An Electrical Instrument for Detecting Invisible Flaws in Nonmagnetic Conductors Such as Tungsten
Authors: Dana D. W.
Published: February 2005

In this instrument the conductor being inspected is passed axially through a coil forming a part of the tuned circuit of an oscillator. Any flaws in the conductor cause a change in the tuning, and thus in the frequency generated, which is conveniently observed through heterodyning with a fixed frequency. By using high frequency, of the order of 6000 kilocycles, the response is limited to flaws near the surface of the conductor. This instrument is used in the factory inspection of tungsten wire, particularly for the location of longitudinal cracks, and is also effective in the determination of asymmetry of coated wires.
Dielectric Power Factor Measurements at Audio- and Radiofrequencies
Authors: Sommerman G. M. L.
Published: February 2005

The paper presents a description of sensitive and accurate apparatus for measuring the power factor of dielectrics in the frequency range, 60–7,200,000 c.p.s. A Wien bridge with Wagner ground for the direct measurement of both power factor and frequency in the range, 60–10,000 c.p.s. is described. Double shielding of the series resistance arm eliminates errors otherwise inherent in this bridge. The operation of the resonance-substitution method is discussed for the frequency range, 10,000–7,200,000 c.p.s. Errors due to eddy current losses are eliminated through measurements on loss free liquids. A measuring cell for use with these circuits and also with d.c. measuring circuits is described. Some experimental power factor-frequency curves illustrating the results obtainable with this apparatus are presented. It is shown that power factor-frequency data furnish a delicate method of tracing out dispersion phenomena and are useful where the concentration or electric moment of material producing dispersion is small.
Voltage Stabilizer Controlled by a Thermionic Pentode
Authors: Evans Robley D.
Published: February 2005

A voltage stabilizing circuit employing one thermionic pentode vacuum tube and one standard 45 v dry battery is described. When used in connection with a conventional a.c. to d.c. rectifier the stabilizer fully compensates for fluctuations in the a.c. mains and provides a d.c. output of zero to several thousand volts in which the fluctuations are less than 1 part in 5000. No current is drawn from the dry battery, hence its useful life is a year or more. Circuit constants are given for stabilizers supplying 85, 135, 600, 1000 and 1400 volts at currents from 15 to 0.5 milliamperes. A general theory of all similar triode, tetrode and pentode stabilizer units is derived, and the impracticability of eliminating the single dry battery is pointed out.
Practicality of Etched Quartz Crystals for X-Ray Spectrometers
Authors: Parratt Lyman G.
Published: February 2005

With a vacuum two-crystal spectrometer the (1, −1) curves of etched quartz, etched calcite and relatively poor calcite cleavage surfaces have been studied throughout the wave-length range 0.5 to 5 Angstroms. The widths of the curves at half maximum intensity, the percent reflection, and the coefficient of reflection have been measured. The shapes of the (1, −1) curves vary with wavelength but vary oppositely with quartz and with calcite. The study is primarily concerned with the possibilities of etched quartz as spectrometer crystals. The resolving power of x-ray spectrometers can be increased by a factor of 2 to 4 by using quartz instead of calcite but the diminution of intensity necessarily associated with such an increase in resolving power may be impractical except for studying relatively strong characteristic radiation.
Photoelastic Apparatus at the California Institute of Technology
Authors: Brahtz J. H. A.
Published: February 2005

A description is given of the reflector polariscope built at the California Institute of Technology. The preparation of models and the technique is explained. Examples of systems of isochromatics and isoclinic lines obtained in models of the Pine Canyon Dam, California, are reproduced.
A Modified Optical Arrangement for Photoelastic Measurements
Authors: Goetz Alexander
Published: February 2005

A modification of the usual apparatus for photoelastic measurements is described in which the large convex lenses on both sides of the specimen are replaced by concave mirrors. The advantages lie in the absence of chromatic aberrations (isochromatic method) and inhomogeneities due to local anisotropies in the lenses; furthermore the price of the apparatus is cut to a fraction. The aberrations of the mirrors—astigmatism and coma—can be made negligible by the symmetrical arrangement of the optical paths and by proper choice of the optical ratio.
Note on the Resonance Radiometer
Authors: Hardy J. D.
Published: February 2005

Experimental evidence in support of Van Lear's theory concerning the Brownian error of the resonance radiometer is given with photographic records showing the character of the baseline unsteadiness. A comparison between critically damped galvanometer systems and the resonance radiometer from an experimental point of view is offered.
An Optical Osmometer
Authors: Dwight C. H. , Kersten H.
Published: February 2005

An osmometer is described which makes use of an optical lever for measuring rapid changes in volume of a solution in osmosis, and which is capable of being read at a distance and of magnifying the readings.