The velocity of sound in liquid helium under its vapor pressure has been determined by an ultrasonic method over a temperature range from 4.22°K to 1.76°K. From. the measurements obtained, the compressibility of the liquid helium has been computed. At temperatures not too close to the X-point, the values are in fair agreement with those estimated from thermodynamical considerations, but the expected discontinuity at the X-transition has not been observed.

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In passenger aircraft flying above 10,000 ft. large quantities of oxygen have to be carried for breathing purposes. An important reduction in weight can be effected by carrying the oxygen supply in the form of liquid, rather than in gas cylinders. It is then necessary to provide means of evaporating the liquid. Various methods of evaporation are discussed, and the liquid-oxygen evaporator developed at the University of Toronto for the Royal Canadian Air Force is described. In this apparatus the heat of evaporation is obtained from the surrounding atmosphere, and the gas pressure is automatically controlled, so that the rate of supply of gas is determined by demand. Successful test flights have been carried out, including one journey across the Atlantic.

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reports sho111d not exceed 600 words a d , for atly issue, sl~ozild be sribi~zitted ?lot later than sir weeks previous to t l~e j 5~s t day of thr rnontl~ of issue. N o proof will be sent lo the authors.A M e t h o d of C o n c e n t r a t i n g He3-He' Mixtures ?\ method has been cle\:eloped for increasing the concentration of He3 in He' from 290 to