540 SECTIONAL TRANSACTIONS.— A. 



the pressure (gpihj) required to force the meniscus in the capillary down to the lo^rer 

 end of the immersed tube. The working formula may be written as 



"■-ki'-d^t 



where A stands for J . 



'jr 

 Hence if the tube is immersed to a depth equal to one-third of the radius, y may be 

 deduced independently of any knowledge of the density of the liquid under test. 

 More generally, if observations of different values of hi and h are made, a plot of h^ 



against ( A — - ) yields a linear graph from the slope and intercept of which accurate 



value of both y and p may be determined. 



Similar considerations apply to the method described some time ago {Proc. Phys. 

 Soc. 36, 37, 1923) for the measurement of y for a liquid obtainable only in small 

 quantities of the order of a few cubic millimetres. A column of liquid of length h 

 is contained in a vertical capillary, and the pressure (gpihj) is measured which is 

 required to force the column down the tube until the lower meniscus is plane at the 

 lower end of the capillary. We then have 



Pi V -V pi 

 and we can similarly obtam a rectilinear plot giving values of y and p for a liquid 

 obtainable in small quantity only. 



Department of Cosmical Physics. 



Dr. F. J. W. Whipple. — The Propagation of Air Waves to great Distances 

 in relation to the Constitution of the Upper Atmosphere. 



The sound of a great explosion can usually be heard at distances exceeding 

 200 kilometres. The source of sound is surrounded by an inner zone of audibility, and 

 beyond a zone of silence there is an outer zone of audibility. Generally the outer 

 zone does not completely surround the source. 



To investigate the phenomenon explosions have been produced at known times 

 and apparatus sensitive to inaudible air-waves has been developed. From a knowledge 

 of the times taken to reach different distances in the outer zone, or zone of abnormal 

 audibility, the velocity of the air-waves at various heights can be deduced. The 

 observations indicate that the heights reached by the waves are usually between 

 40 km. and 50 km., and that the velocity of sound at such heights is greater than near 

 the ground. Thus the observations support the theory of Lindemann and Dobson, 

 according to which there is warm air above the stratosphere. 



It is hoped that further observations will make it possible to follow the changes 

 in the condition of this warm part of the atmosphere. Hitherto the investigation 

 has been carried on most vigorously in Germany, but systematic observations have 

 been made in England during 1927 and 1928, the origin of the air-waves being a 

 16-in. gun in the Isle of Grain. The most successful receiving stations are at 

 Birmingham and Bristol at ranges of 213 km. and 230 km. respectively. Hot-wire 

 microphones are used. 



The time of passage of the air-waves to Birmingham has varied between 

 11 mins. 48 sees, and 12 mins. 18 sees. Eor Bristol the departures from the average 

 time 12 mins. 53 sees, have been small. Observations giving the angle of descent 

 of the air-waves have been made at these two stations recently. It is found that 

 the waves reaching Birmingham have the flatter trajectories. The interpretation 

 of observations from a couple of stations is uncertain owing to the impossibility of 

 allowmg for wind. If this factor be ignored the observations at Bristol and Birming- 

 ham on May 11, 1928, indicate that the uniform temperature of the stratosphere 

 extended to 30 km. above ground, and that the temperatures at 40 km. and 50 km. 

 were about 15° C. and 70° C. respectively. 



Mr. G. A. Clarke. — The Association of Cloud with Weather. 



