Year: 1874

halnIau Dy Flr1ng or Artillery.

 Prof. Edward Powers, of Chicago, is engaged in endeavoring to demonstrate the p~acticability of controlling and dis tributing rainfall by means of concus- sions produced by the firing of artillery This subject, if not entirely new, is of great importance, and should be thor oughly investigated by the govern ment. Our Western domain, to say nothing of the vast desert wastes of other portions of the earth, demands irrigation. General Grant called atten- tion to this necessity in his recent Mes- sage. MT. Powers theory is deduced from an examination of one hundred and thirty battles that were succeeded by copious rains. He claims that about sixty per cent. of all battles or bom- bardments of importance are followed by rain within the first twenty four hours from the commencement of the heavy firing. A calculation made from the observed average number of rainy days in the year when there are no bat ties shows that only thirty two per cent. would be so followed within that time if the battles had no influence in pro- ducing the rain. About ninety per cent. of such battles are followed by rain within the first forty eight hours after the commencement of the heavy firing. All great battles in which much artillery was used were followed by rain (so far as definite information can be obtained.)

 The average length of time between the commencement of the heavy firing and the beginning of the rain is twenty six and half hours. Rain following great battles, in which much artillery is used, is almost always very heavy. En- agreements other than great battles, in which much artillery is used, are also generally followed by heavy rain, but musketry firing does not bring much rain. Rains follow battles not only in the spring and summer, but also in autumn and winter. Rains follow bat ties not only in this country and ln Flu rope, but in the dry season in Mexico. Heavy rains follow great battles fought in times of drought. The rains follow ing battles are generally accompanied with thunder and lightning. The the ory of rain generally accepted by phi losophers is that it is produced by the union of two bodies of air, one of which is colder than the other, and both satu- rated with aqueous vapor. It has been proven by experiments that when two such bodies of air are mixed, they can- not, when mixed, contain as much vapor as they did before, the reason for which is explained by the principle that warm air has Q greater capacity for vapor than cold air, and that this capacity dimin- ishes in a much greater ratio than the take up large quantities of vapor from the ocean, which vapor is carried north and south by the equatorial currents. Hence there are generally above us cur rents of warm air saturated with vapor.

 To explain how cannon firing pro- duces rain, it is only necessary to ex- plain how these currents are caused to mix with the colder currents above them. The explanation is that it does so by rarifying the hnmid current. It rarifes it by condensing a small portion of the vapor which it contains. It con- denses this small amount of vapor by concussion, which is similar to sudden pressure, and we know that by pressure aqueous vapor is condensed and it's latent heat is given out-that is, when cannon firing brings rain there is con- densation of vapor in two ways first, i little condensation by the pressure of the shocks of concussion, which causes an evolution of heat and ratification of the air, and, second, a great con- densation caused by the rise of the humid current and it's mixing with the colder one above it. As 1t will natur- ally take little time for an air current hundreds, and perhaps thousands, of feet in thickness to rise into the colder corrent after being rarifed by the con- cussions, and as, in the meantime, the air so rarifed will be carried along by the current, it follows that the rain will not commence at the place where the firing takes place. It will generally work back to that place in the path of the current, however, arriving, as be- fore stated, in an average time of twen- ty-six and one-half hours from the con- mencement of the firing. Unless the firing is heavy and continued for two or three hours, so as to rarify larger area and volume of the air current as it passes over, there will be no rain, or if there is rain somewhere on the path of the air current it will not reach the place where the firing takes place, as the equilibrium between the two cur rents will be restored before the rain reaches that point.