﻿EQUIPMENT AND WORK OF AN A EKO-PHYSICAL OBSERVATORY. 9 



be accomplished. The exploration of the upper air by " aerodromoi " 

 means the determination of abnormal temperature and rainfall relations 

 at various heights. 



Claudy Condensation. — Perhaps even more than temperature, rain is the 

 element of least certainty in forecasting. How, then, can we improve the 

 methods in use for foretelling the likelihood and determining the causes 

 of rain? Of the phj^sical processes of condensation we know much and 

 at the same time little. Studies of condensation from fusion, vaporiza- 

 tion, and solution, and particularly on the passage from vapor to liquid 

 in the free air and the control of the conditions determining such passage^ 

 should be undertaken. With our present rather crude outfits some work 

 might be done in the nature of preliminary surveys of cloud land. At 

 present cloud maps are of such indefiniteness that but limited use is made 

 of them in forecasting. Granted that cloud types and motions have little 

 of the significance that some enthusiastic nephoscopists claim for them, 

 the fact nevertheless remains that clouds from their very office are signifi- 

 cant exponents of air-strata conditions. Hildebrandsson long ago showed 

 that the upper currents move along somewhat parallel to the lower cur- 

 rents up to a certain height, and then change their motion, and we are 

 all familiar with Clement Ley's law, " upper clouds have a distinct cen- 

 trifugal tendency over areas of low pressure, and a centripetal over those 

 of high." If we knew more about cloud motion and stratification, fore- 

 casting would be more certain. 



To illustrate in a rough way the importance of cloud motion, let us take 

 the date August 27, 1893, a time when telegraphic reports from Florida 

 and the southeastern seaboard were interrupted. It is evident that if no 

 reports can be obtained by telegraph, the synoptic map as at present 

 used must fail. Such was the case during the memorable storm of March 

 11-13, 1888— the so-called '^ blizzard." But in the storm of 1893 it so 

 happened that the most destructive storm of the year was heading in 

 towards the Florida coast. No reports were to be had from Florida, high 

 wdnd having blown down the poles. What, then, was the forecaster to 

 do ? The motions of the upper clouds at Lynchburg, Chattanooga, Knox- 

 ville, and Norfolk plainly indicated the position of the " low." If, with 

 such crude and undeveloped observations, there was so much of value 

 in cloud-work, with how much more definiteness could this storm have 

 been located had the motions of the upper clouds at various points 

 been instrumental determinations. One much-needed advance in fore- 

 cast work is the use of nephoscopes, and it is passing strange that our 

 weather services have not long ago discarded their methods of eye ob- 

 servation. Color, form, and relative motion appeal so strongly to tlie 

 imagination that even a practiced observer will misinteri)ret the cloud. 



