NATURAL RAIN-MAKERS. 



645 



Great progress has been made in the past five years in our 

 knowledge of clouds. Two masters in physical science, von Helm- 

 holtz and Hertz, were brilliant cloud investigators. The for- 

 mer explained the formation of cloud billows ; the latter devised 

 a graphic method of following the adiabatic changes in moist air. 

 The number of tiny solid particles in a cloud can even be counted. 

 John Aitkin, of Edinburgh, has constructed a dust-counter deli- 

 cate enough to do this. The dust nuclei in the smoky air of Lon- 

 don, on the quiet shores of the Mediterranean, on Alpine peaks, 

 or in the pure mists of the Scotch Highlands can be counted and 



Fracto-nimbus. Advance Clouds of Thunderstorm. 



their influence in the making of rain properly appreciated. Both 

 in Europe and the United States meteorologists are studying 

 clouds. At Berlin, Storlein, Upsala, and Blue Hill observers are 

 daily determining cloud heights and velocities, and in the coming 

 year forces will be massed and something akin to a systematic 

 survey of cloudland attempted. 



Poet, painter, and all of us have felt the keen delight of fol- 

 lowing the cloud transitions of a summer sky. All men in all 

 lands are nephelolaters or cloud admirers for the cloudscape 

 gives all that the most varied landscape can offer. A generous 

 sky knows no difference between the sons of earth, and spreads 

 everywhere scenes of wondrous grace and color. Even the most 



