The St. Johns herald., 1891-10-15
Gan We Make 1t Rain?

do maintain two propositions. l
 We are ever going to make 1t rain
 or produce any other result hitherto unattainable, We must employ ade- quate means. And if any proposed means or agency is already familiar to science, we may be able to de eide beforehand whether 1t is ade- qpate. Let us grant that out of a thousand seemingly visionary pro- jects one is really sound. Must we try the entire thousand to find the one? By no means. The chances are that nine hundred of them will involve no agency that is not al- ready fully understood, and may, therefore, be set aside without even being tried. To this class belongs the project of producing rain by sound. AS 1 write, the daily jour- nals are announcing the brilliant success of experiments in this di- rection; yet unhesitatingly main tain that sound cannot make rain, and propose to adduce all necessary proof of my thesis. The nature Of sound is fully understood, and 30 are the conditions under which the
 aqueous vapor in the atmosphere may be condensed. Let us sec how the case stands. A room of ave- rage size, at ordinary temperature and under usual conditions, con- tains about quart of water in the form of invisible vapor. The whole atmosphere is impregnated with va DOT in about the same proportion. We must, however, distinguish be- tween this invisible vapor and the clouds or other visible maeses to which the same term is often ap- piled. Clouds are not formed of true vapor, but consist of impalpa- ble particles of liquid water float ing or suspended in the air. But we all know that clouds do not always fall as rain. In order that rain may fall the impalpable particles of water which form the cloud must collect into sensible drops large enough to fall to the earth. Two steps are therefore necessary to the formation ot rain; the transparent aqueous vapor in the air must be condensed into clouds, and the ma terial of the clouds must ag- glomerate into raindrops. No phy- sical fact is better established than
 that, under the conditions which prevail in the atmosphere, the aqueaus vapor of the air cannot be condensed into clouds by compress sion. But, for reasons which need not explaiR, condensation by com. pr ipn cannot take place in tho air, The cooling which results in
 the formation of clouds and rain
 may come in two ways. Rains which last for several hours or days are generally produced by the inter mixture of currents of air of diff ferent temperatures. A current of cold air meeting current of warm, moist air in it's course may con dense a considerable portion of the Q moisture into clouds and rain, and this condensation will go on as long as the currents continue to meet. In hot spring day a mass of air
 which has been warmed in the sun, and moistened by evaporation near the surface of the earth, may rise up and cool by expansion to near the freezing point. The resulting condensation of the moisture may then produce shower or thunder squall. But the formation of clouds in clear sky without motion of the air or change in the tempera- ture of the vapor is simply impos- sible. We know by abundant ex
 periments that a mass of true aqueous vapor will never condense into clouds or drops so long as its temperature and the pressure of the mir nnon if remain unchanoed Nov