... Old ... Is Formed

To u. rttand the philo-ophy of thiê plienoreenon, uesttnüal . the very existsuee of planta and animale, a lew facts, dcrived f rom observatiun and a long train of experimenta, must be remcmbered, Were tho atroosphere everywhere, at all linies, at a uniform tnnperature, we nbould oever have rain, hail, or cnow. Tho water absorbed by it in evaporation from tha se and the earth's surface would descend in au iuiperceptibla va por, or.cease to be absorbed by the nir wbeu it wiis once fully saturatcd. The abaorbing power of the atmoHpliere. and conpequeutly ita capabilily to retnio humidity, is proportiouably greater in sold tban warm air. 'i'be air near the itnrface ot the enrth is warmer than it is iu the región of the olouds. The higher we asceod from the earth, the ooider we ind the atmosphere. Henea the perpetual Hiiow on very high mouutains, iu i4ie hottest climates. Now, when froin evsportion the air is Litjhly saturated with vapor, - though it ba invisible, - if its temperature is suddetily reduced by cold currenti descen'ling from above, or rushing from a higher to a lower Utitudu, ita capacity to retain moisiure is dimiuishud, olnud are foruied, and tbe result i riu. Air cundt-DSes as it cools, aud like a epoago filled with water and coinpresed, pnurg out water which its dimiuished capacity cannot hold. How singular jet bw tiuiple Í8 such an arrangement for wateriug the earih ! - Soientifio American,