McAdie — Wew Units in Aero-physics. 279 



thermal conditions up to 27 kilometers. Tiessereiie de Bort* 

 has shown that " the stratosphere is lowest in tlie cyclone and 

 liighest in the anti-cyclone, and its level sinks from the equa- 

 tor to the poles. Tiie stratosphere is a region of interlaced 

 currents and small vertical movements." 



The term isothermal has heen applied to the i-egion above 

 11 kilometers to distinguish it from the lower levels or tropo- 

 sphere in which "the vertical variation of temperature is 

 about 6° C. per thousand meters. "f The names advective and 

 convective have also been suggested as indicating the modes of 

 transfer of tlie aii" in the two great divisions of the atmosphere. 



The work now in progress on the exploration of the upper 

 air and the prevalent interest in aviation open a new era in 

 aerology. The promise of the times is a more definite knowl- 

 edge of pressures and temperatures at all levels. It is^ there- 

 fore, of some importance that our present bewiklering systems 

 of notation should give way to one international nomenclature. 

 Our present cumbersome and inadequate units should be 

 replaced by others capable of conversion into absolute units 

 and suitable for' universal needs. We think the new unit, 

 whereby atmospheric pressure is recorded in dynes, meets the 

 requirements. 



Temperature. 



Since the time of Galileo temperature has been measured by 

 the expansion of mercury in a glass tube. The unequal 

 expansion is divided into degrees and values are based upon 

 the position of two fiducial points. Without going into the 

 evolution of present thermometric scales, it may be noted that 

 Galileo had a scale of 360 degrees, the lowest point based upon 

 some freezing mixture and the highest representing tlie warm- 

 est day of sunnner. Fahrenheit had several scales. In the one 

 finally adopted the zero is based on the temperature of the 

 coldest day of the year 1709 in northern Europe. Reaumur 

 used melting ice and boiling water, dividing the distance into 

 eighty degrees. Celsius, using the same points, divided the 

 distance into one hundred degrees, with the zero at the boiling 

 point. This scale is often referred to as identical with the 

 Centigrade scale, but this is a mistake. Linnseas modiiied 

 Celsius' scale, making the zei'O indicate the temperature of 

 melting ice and one hundred degrees that of boiling water. 

 This is the widely used Centigrade scale. Concerning the 

 Fahrenheit scale it may be noted that it has practically lost 

 place in scientific usage to-day. Furthermore, in all our ther- 

 mometric scales the so called fixed points are not truly fixed. 



* Eeport of Aerological Congress at Monaco, 1909. Eotch in Science, 

 Tol. XXX, No. 763, p. 193-199, August. 1909. 

 t Gold and Harwood, B. A. A. S., 1909, p. 33. 



