r.tl;'.] The Winds in the Free Air 717 



WEEKLY EVENING MEETING, 



Friday, April 11, 1913. 



The Ri(4HT Hon. Lord Rayleigh, O.M. P.C. D.C.L. 

 LL.T). F.R.S., in the Chair. 



Charles J. P. Cave, Esq. M.A. J.P. M.R.I. 

 The Winds in the Free Air. 



It was noticed in very early times that the wind in the upper air 

 may be very diiferent from what it is on the surface. Lucretius 

 says : " See you not too, that clouds from contrary winds pass in 

 contrary directions ; the upper in contrary way to the lower." Bacon 

 advocated the use of kites in studying the winds ; but it is only in 

 (juite recent years that any systematic attempt has been made to 

 investigate the free air above the surface of the earth. Kites have 

 been flown to a lieight of fo'ir miles, but it is a matter of some 

 delicacy to get even as high as two miles. 



The temperature of the free air may be recorded by a meteoro- 

 graph attached to a small rubber balloon, which continues to ascend 

 until the pressure of the gas inside bursts the envelope, and the 

 instrument descends again to the surface. The beautiful instrument 

 constructed by Mr. W. H. Dines, F.R.S., the pioneer of upper air 

 research in this country, is so light that the torn fabric of the balloon 

 is sufficient to act as a parachute and check the speed of descent. 



The general result of the observ^ations has been to show that the 

 temperature of the air decreases with height up to a certain point, 

 above which the temperature distribution is nearly isothermal ; how- 

 ever much higher the balloon may ascend, there is little further 

 cliange of temperature. This upper layer, discovered by M. Teisserenc 

 de Bort, whose recent death meteorologists of every countiy lament, 

 is called the Stratosphere ; the lower part of the atmosphere is the 

 part that is churned up by ascending and descending convection 

 currents and is called the Troposphere. The height at which the 

 Statosphere is reached, as well as the temperature of the layer, varies 

 from day to day and from place to place. In these latitudes it is 

 met with at heights varying from about 8 to 14 kilometres, with 

 temperatures varying from - 40° to - 80" Centigrade. 



It is not, however, with temperatures that I am chiefly concerned 

 to-night, but with the wind currents in the different layers of the 

 atmosphere. If one of the balloons carrying instruments, or a smaller 

 pilot-balloon, is observed with a theodolite, its position from minute 



