摘要:

The refractive indices of liquid Helium I and Helium II were measured by means of a Wollaston cell. The value obtained with λ5461 Å for He I at 4.2° K was 1.0206 ± 0.0012; for He I at 2.26° K, 1.0269 ± 0.0004; and for He II at 2.18° K, 1.0269 ± 0.0004. It was also shown that the index changed by less than ± 0.00007 in passing from a point in He I to a point with the same density in He II. It was concluded, therefore, that there is no change in the molecular refractivity in passing from He I to He II.

ISSN:1923-4287    

DOI:10.1139/cjr38a-014

出版商:NRC Research Press    

年代:1938

数据来源: NRC

摘要:

A new form of helium gas thermometer is described, which is designed for permanent installation in low temperature equipment in order to cover the difficult region between the temperatures of liquid hydrogen and of liquid helium. The device departs radically from the usual gas thermometer practice by having the volume of gas which remains at room temperature considerably larger than that of the thermometer bulb proper. It is shown theoretically that by this means the sensitivity, as compared with that of an ordinary gas thermometer with the same initial pressure and temperature, is greatly increased at the lowest temperatures. Thus it is possible to construct a thermometer which is sufficiently sensitive in the region below 20° K. to read temperatures to within 0.1° with the aid of an ordinary mercury manometer, and yet have a pressure only of the order of one atmosphere at room temperature. An experimental test has shown that the device is entirely practicable.

ISSN:1923-4287    

DOI:10.1139/cjr38a-015

出版商:NRC Research Press    

年代:1938

数据来源: NRC

摘要:

When the mass of unit length of a string of length 2L, instead of being uniform, increases from the centre toward the ends according to the law (1 + x/L)m, the natural frequencies of vibration are lower than those of the uniform string, but the ratios between the frequencies of successive overtones remain virtually unchanged, and with the exception of the first one or two overtones agree with those of a uniform string having a mass per unit length (2(1 + λ)(m+2)/2 − 1)/λ(m + 2) times that at the centre of the strengthened string. The reduction in the natural frequencies of vibration is, of course, larger the greater the ratio between the masses at the two ends, whereas the value ofmhas a relatively small influence. The overtones form two distinct series: one, corresponding to the harmonics of even order, is always present; the other, corresponding to the harmonics of odd order, is suppressed when the density of the string increases from one end to the other (unsymmetrical span).

ISSN:1923-4287    

DOI:10.1139/cjr38a-016

出版商:NRC Research Press    

年代:1938

数据来源: NRC