Page:Popular Science Monthly Volume 47.djvu/661

Rh Great progress has been made in the past five years in our knowledge of clouds. Two masters in physical science, von Helmholtz and Hertz, were brilliant cloud investigators. The former 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 delicate enough to do this. The dust nuclei in the smoky air of London, on the quiet shores of the Mediterranean, on Alpine peaks, or in the pure mists of the Scotch Highlands can be counted and



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 following 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