Volume 3, Issue 3, March 1932
Index of content:
3(1932); http://dx.doi.org/10.1063/1.1748912View Description Hide Description
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.
3(1932); http://dx.doi.org/10.1063/1.1748916View Description Hide Description
An air‐cooled electromagnet for work in Zeeman effect has been constructed due to lack of a `soft' water supply for cooling. The pattern of the instrument follows the Boas type, but includes a number of improvements. The yoke is made of a wider cross section, thus eliminating the narrowing of the pole gap upon application of the field. The current is carried by 2000 turns of flat bare copper ribbon wound in 24 pancake coils which are cooled by a forced draft of air circulated between the coils by a fan. Temperature equilibrium is reached throughout the instrument in less than an hour, and in half an hour in the pole‐gap where the temperature rise is about 5°C for an inducing current of 20 amps. Using ferro‐cobalt pole caps with pole face of 8 mm diameter, fields of 39500 gauss and 43500 gauss were obtained respectively for gaps of 4 mm and 2.4 mm with a current of 25 amps. For a gap of 1 mm and a current of 33 amps, a field of 48500 gauss was reached. Zeeman patterns were produced corresponding to nearly full strength of the magnetic field with no loss in sharpness, due to thermal fluctuations even during the first hour of application of the field.
3(1932); http://dx.doi.org/10.1063/1.1748918View Description Hide Description