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Sep 1938

Volume 9, Issue 9, pp. 263-284

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The Limiting Sensitivity of an Alternating‐Current Method of Measuring Small Magnetic Moments

E. A. Johnson

Rev. Sci. Instrum. 9, 263 (1938); http://dx.doi.org/10.1063/1.1752549 (4 pages) | Cited 18 times

Online Publication Date: 27 December 2004

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A method of measuring the moment of small magnetic dipoles is described. The dipole to be measured is rotated inside of a fixed coil, and the voltage induced in the coil is measured by means of an alternating‐current amplifier. The limiting sensitivity is computed from the calculated signal‐voltage and the thermal agitation in the input circuit. In the practical application the theoretical sensitivity is approximately obtained and moments of 3×10−7 c.g.s. unit can be detected and with a specimen 1.5 cm on a side 8×10−8 c.g.s. unit/cc can be detected. The method has been applied to the measurement of the polarization in sedimentary deposits.

Some Experiments on the Amplification of Thermocouple Electromotive Forces

Ross Gunn

Rev. Sci. Instrum. 9, 267 (1938); http://dx.doi.org/10.1063/1.1752550 (3 pages) | Cited 7 times

Online Publication Date: 27 December 2004

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Experiments employing a new type of regenerative direct‐current amplifier have shown that such equipment is unsuited for use, except, perhaps, in the laboratory. A successful system of amplification employing vacuum tube amplifiers and commutators for inverting and synchronously rectifying the resulting amplified alternating potentials is described. Thermocouple electromotive forces less than 10−9 volt are readily indicated on a portable microammeter. The over‐all useful amplification with portable equipment exceeds 50,000.

A Push‐Pull‐Stabilized Triode Voltmeter

Charles Williamson and John Nagy

Rev. Sci. Instrum. 9, 270 (1938); http://dx.doi.org/10.1063/1.1752551 (3 pages)

Online Publication Date: 27 December 2004

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This general purpose, balanced triode voltmeter is stabilized by adjusting shunt resistors until the effective values of μ and Ip are the same for both tubes. Built‐in testing equipment is provided. The electrical zero of the galvanometer is unaffected by changes of ±20 percent in power‐supply voltage when the circuit has a d.c. sensitivity of 40,000 mm/volt. The tubes need not be specially selected. The balancing principle may be adapted for use in any circuit requiring matched tubes.

An Electronic Null Detector for Impedance Bridges

Horatio W. Lamson

Rev. Sci. Instrum. 9, 272 (1938); http://dx.doi.org/10.1063/1.1752552 (4 pages) | Cited 4 times

Online Publication Date: 27 December 2004

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A Thyratron‐Controlled Thermostat

Julian M. Sturtevant

Rev. Sci. Instrum. 9, 276 (1938); http://dx.doi.org/10.1063/1.1752553 (4 pages) | Cited 11 times

Online Publication Date: 27 December 2004

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An Electrostatic Method of Measuring Elastic Constants

Dennison Bancroft and Robert B. Jacobs

Rev. Sci. Instrum. 9, 279 (1938); http://dx.doi.org/10.1063/1.1752554 (3 pages) | Cited 11 times

Online Publication Date: 27 December 2004

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Electronic Emission From Vacuum Tube as Substitute for Battery

Robert B. Taft

Rev. Sci. Instrum. 9, 282 (1938); http://dx.doi.org/10.1063/1.1752555 (1 page)

Online Publication Date: 27 December 2004

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The Permanence of Absorption Weakeners of Antimony

G. O. Langstroth and D. R. McRae

Rev. Sci. Instrum. 9, 282 (1938); http://dx.doi.org/10.1063/1.1752556 (1 page)

Online Publication Date: 27 December 2004

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PHYSICS NEWS

Rev. Sci. Instrum. 9, 283 (1938); http://dx.doi.org/10.1063/1.1752557 (2 pages)

Online Publication Date: 27 December 2004

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