DISCOVERY 



77 



milky liquids, and on being further heated these 

 mUky liquids become clear at definite temperatures. 

 When these liquids are cooled, the phenomena are 

 reversed. In addition to their turbid appearance, 

 these milky Uquids exhibit strong double refraction, 

 and the term ' ' crystalline liquids ' ' has been applied 

 to them. Much discussion has taken place with 

 reference to the justifiability of this term. Greater 

 interest, perhaps, is attached to liquid sulphur. When 

 sulphur is melted, it fuses to an amber-coloured 

 liquid, but on being further heated, it becomes 

 much darker and more viscous. It has been shown 

 that this phenomenon is due to the fact that liquid 

 sulphur is not a single substance, but a mixture 

 of two different liquids in d;yTiamic equilibrium. The 

 proportion of these two liquid forms varies with the 

 temperature. Smits, who has given much attention 

 to the theoretical aspects of polymorphism, considers 

 that the case of liquid sulphur is to be regarded as 

 one of djmamic aUotropy, an idea similar to that of 

 dynamic isomerism (reversible isomeric change), 

 familiar to organic chemists. 



BIBLIOGRAPHY 



The Theory of AUotropy, by A. Smits; translated b}' J 

 Smeath Thomas, 1922. 



How Upper Winds are 

 Measured 



By C. E. Britton, B.Sc. 



It is a matter of common observation that clouds 

 often proceed from a different quarter from the wind at 

 the ground, and in most cases appear to be carried 

 along at much greater speed than that of smoke from 

 chimneys. In other words, the speed and direction of 

 the wind in the upper air is often different from the 

 speed and direction of the surface wind. In fact it is 

 very imusual to find the wind at a point 10,000 feet 

 above the ground to be the same, either in direction 

 or speed, as the wind experienced at the same instant 

 on the surface. 



Recent Causes effecting Upper Air In- 

 vestigations 



.\lthough this difference in the wind at various 

 heights in the atmosphere has been known for a long 

 time, it is practically only within the last twenty-five 

 years that the velocity of these upper winds has been 

 scientifically measured. At first, upper air investiga- 

 tions were only undertaken b}^ research workers, but. 



as the importance of the aeroplane came into promin- 

 ence, measurements of upper winds began to be made 

 at flying schools. It was the Great \\'ar, however, 

 which made the continuous and extended observation 

 of the upper atmosphere both necessary and possible. 

 Requests for upper wind readings came from many and 

 various directions. The rapidly increasing bands of 

 aviators required the information ; the artiUer^Tnan 

 wanted it to ensure accuracy in his firing ; the gas war- 

 fare departments were equalh* interested, and it was 

 of the first importance to the sound-rangers. These 

 represented but a few sections of the forces who found 

 of the greatest use the information gleaned by the 

 meteorologists. As a result of this unparalleled ex- 

 pansion, there is now a network of stations in this 

 country where observations of upper winds are made 

 three or four times daily, and the results are embodied 

 by the Air Ministry in a special " Upper Air Supple- 

 ment of the Daily Weather Report." 



Usual Procedure of Investigation 



The method of upper wind measurement in general 

 use consists essenticJly in releasing a small rubber 

 balloon filled with hydrogen and following its sub- 

 sequent journey by means of a special instrument 

 to measure angles, known as a theodolite. There are 

 several types of balloon used for the purpose, but the 

 one in most common use is made of very thin sheet 

 rubber weighing just over an ounce ; it is inflated with 

 hydrogen until its diameter is about 2 feet. The rate 

 of ascent of such balloons in still air has been found 

 to be ver}^ nearlj- uniform, and J. S. Dines ^ has given 

 an empirical formula connecting the rate of ascent with 

 the weight of the balloon and the mass it will just lift 

 when inflated. For the t\'pe of balloon mentioned 

 above a velocity of ascent of about 500 feet per minute 

 is obtained, and the usual practice is to adjust the 

 amoimt of gas put into the balloon so that its rate of 

 ascent, on the basis of the formula, shall be exactly 

 500 feet per minute. 



The flight of these balloons (pilot balloons, as they 

 are called) is watched by an observer through a theo- 

 dolite designed for this special purpose. These instru- 

 ments are so designed that the observer is always 

 looking in a horizontal direction, however much the 

 balloon may move about in the sky, and the tangent 

 screws moving the telescope are constructed so that 

 rapid motion can be secured to keep the balloon in 

 the field of view. 



The first step in the process of making an observa- 

 tion consists in the setting up of the theodolite. After 

 leveUing the instrument, the telescope is sighted upon 

 a prominent object in the landscape, the bearing of 

 which is known, and the scale is revolved untU a fixed 

 ' OJ.R. Met. Soc, 1913 and 1918. 



