December 23, 1904.] 



SCIENCE. 



875 



tries. While, naturally, much less is 

 known regarding the circulation of the 

 upper air, a great deal has been ascertained 

 from the observations of clouds that were 

 instituted a few years ago in various parts 

 ■of the world by an international committee. 

 In order to insure that the same cloud 

 should everywhere be called by the same 

 name, it Avas necessary to instruct the ob- 

 servers by publishing a cloud-atlas, con- 

 taining pictures and descriptions of the 

 typical forms of clouds which experience 

 has shown to be identical all over the globe. 

 Then during one year which had been 

 agreed upon, measurements of the direction 

 of drift and the apparent velocity of the 

 •several cloud-types were made at many 

 stations, and measurements, by trigonomet- 

 rical or other methods, of the height of 

 these clouds above a few selected stations 

 enabled the true velocity of the air-cur- 

 rents to be determined up to the altitude 

 at which the cirrus clouds float. Thus an 

 actual sui-vey of the direction and speed 

 of the atmospheric circulation at different 

 levels was effected, and a recent discussion 

 of the results by Professor Hildebrandsson 

 ■shows that the theories which have been 

 held heretofore are untenable. Professor 

 Hildebrandsson 's conclusions in brief are 

 that there is no exchange of air between 

 poles and equator, the circulation over the 

 oceans, at least, resolving itself into four 

 great whirls, the air which rises above the 

 tropics flowing over the trades and descend- 

 ing probably in the extra-tropical regions, 

 while around each pole is an independent 

 cyclonic circulation. Although this gen- 

 -eral circiilation of the atmosphere appears 

 to be indicated, many details require to be 

 investigated. In particular, the move- 

 ments of the great masses of air overlying 

 the trade winds and doldrums, which is a 

 region nearly barren of clouds, are still un- 

 Icnofvn and the determination of these 

 movements, as well as the temperature and 



humidity of the different strata, by means 

 of kites flown from steamships, was sug- 

 gested by the writer, since it would be pos- 

 sible in this way to penetrate even the 

 masses of quiescent air which probably 

 separate the trade winds from the super- 

 posed antitrades. This suggestion has 

 already been put in practise on the yacht 

 of the Prince of Monaco in the neighbor- 

 hood of the Azores, but a more extensive 

 campaign is necessary, which the writer 

 himself hopes to undertake, if the funds 

 necessary to charter and equip a steamer 

 can be procured. 



Here it will be encouraging to state some 

 results of the efforts to ascertain the verti- 

 cal thermal and hygrometric gradients in 

 the atmospheric ocean, and to show what 

 may be accomplished in the future. Ob- 

 servations on mountains, as we have seen, 

 can not be expected to give the conditions 

 which exist at the corresponding heights in 

 the free air and hence the necessity of send- 

 ing observers or self-recording instruments 

 into this medium through the agency of 

 balloons and kites. By the aid of an inter- 

 national committee formed eight years ago 

 under the direction of Professor Hergesell 

 at Strassburg, much has been accomplished 

 in Europe in this way, and something in 

 this country through kite-flights. At the 

 present time such atmospheric soundings 

 are made once a month in most European 

 countries, and at Blue Hill in the United 

 States, with the result that a knowledge is 

 being acquired of the vertical gradients of 

 the meteorological elements which entirely 

 contradicts previous conceptions. For ex- 

 ample, it was formerly supposed that the 

 temperature diminished with increasing 

 altitude more and more slowly and that at 

 a height of about ten miles it remained in- 

 variable during winter and summer and 

 above pole and equator. But the recent 

 investigations of my colleagues in France 

 and Germany shoAV that the temperature 



