LOW TEMPERATURES AND REFRIGERATION—MARCHIS. 9138 
apparatus enables him to extract as a by-product of the industrial 
manufacture of oxygen and nitrogen, a mixture of nitrogen with at 
least 50 per cent of neon, helium, and hydrogen. To accomplish 
this the gaseous residues which are strongly resistant to liquefaction 
are drawn out, in the proportion of 6,000 liters per hour for an 
influx of air of 3,500 cubic meters, from the lower parts of a tubular 
system cooled by liquid nitrogen. By the conjunction of a pressure 
of 4 atmospheres and a very low temperature, all the liquefiable 
parts are condensed and the gaseous residue, if the quantity is well 
regulated, consists of an almost pure mixture of neon and helium. 
The liquefaction of air is not the last obstacle which men of 
science have overcome in the field of gas condensation. Helium, 
which long resisted the efforts of all physicists, has finally been 
liquefied by M. Kammerlingh Onnes in the cryogenic laboratory 
at Leyden“ whose installation admits of the attainment of a range 
of temperatures from 0° down to —253°. By cooling down helium 
by hydrogen boiling in a vacuum and suddenly expanding the gas 
compressed to 100 atmospheres, the Dutch scientist has obtained a 
transparent colorless liquid boiling at —269° with a density of 0.154. 
The critical constants of helium appear to be in the neighborhood 
of —268° and 3 atmospheres. 
Thanks to the admirable scientific equipment of the laboratory at 
Leyden, M. Jean Becquerel has been able to study at very low tempera- 
tures the phenomena of liquid absorption and emission, such as the 
magneto-optic phenomena in crystals and solidified solutions. This 
work of Becquerel, so important in its significance, bears on the fol- 
lowing points: 
(1) Observation of the influence of variations of temperature on the 
abnormal phenomena of absorption and dispersion. Laws of the 
variation of the width of bands, and the existence for each band of a 
maximum absorption. Calculation of the number of corpuscles pro- 
ducing absorption. Spectral analysis at low temperatures. 
(2) Study, in crystals and solutions of a phenomenon of the same 
nature as the Zeeman effect. Invariability at varying temperatures, 
of period changes produced by magnetism. Observations at low tem- 
peratures of phenomena showing the variation in stability of vibrat- 
ing systems, where their period is modified. 
(3) Rotary magnetic polarization at low temperatures. Explana- 
tion of rotation in the vicinity of the bands of absorption. Gener- 
alization of the phenomenon of rotary magnetic polarization. Ex- 
tension of the phenomenon to biaxial crystals. Joinder produced by 
a magnetic field, of two principal vibrations, normal to the lines of 
“Mathias: Le Laboratoire eryogene de Leyde. Revue générale des Sciences, 
Paris, vol. 7, 1896, p. 381. 
