We have received a circular bearing the above title trom Daniel Vaughan. His theory ? is as follows :— That electricity partakes of the power of sustaining vapor in the atmosphere is evident from several facts. When allowed to evaporate, the surface of water is not only cooled, but is also rendered negatively electrified, while the vapor itaelt is positive. From this it appears that the vapor is formed at the joint expense of heat and electricity. Experiments also prove that evaporation is retarded whenever the water is insulated ; a result which shows more conclusively the part which the electric fluid aets in the production of vapor. Accordingly the amount of watery vapor which the atmosphere can contain, depends nob only on its temperature, but likewise on its electricity, which, according to all experiments, is much increased in intensity at great elevations, and here its agency becomes important as that ot heat declines.— The evaporation of water and the friction of the air against the surface of the earth, are commonly regarded as the principal sources of atmospheric electricity; and, to render the mechanism of nature more effective for its development and for confining it to the upper regions, an insulator is provided by means of the lower stratum of air which is most free from humidity, for the moist air continually ascends on account of its inferior specific gravity. It is well known that positive electricity is always liberated whenever vapor is condensed ; and, should its escape be prevented by insulation, the condensation will, of course, be retarded. The non-conducting power ot the lower stratum of air will, therefore, be the means of keeping the aqueous vapor dis-sol ved in the atmosphere until the insulation is broken by the near approach of humidity ju the earth's surface or by other causes.— The electricity being then no longer confined by a proper barrier, should escape to the earth; the portion ol vapor which was dependent on its support, should condense, and in most cases, descend as rain; while, at the same time, the drops in approaching the surface of the earth, should saturate the earth with moisture, and thus furnish a means for the more rapid discharge of electricity and the more complete precipitation ot the superfluous water of the atmosphere. In consequence of the humidity of the atmosphere, mountains withdraw electricity from a considerable distance; and by causing the descent of rain open numerous channels by which the electric fluid passes from much greater distances to the adjacent lowlands.— The indirect influence of mountains, therefore, extends many miles around them, and hence it is that they do not themselves receive as much rain as the plains and valleys in their vicinity though their effect on its production is too obvious to be doubted, In the vast island or continent of Australia which contains no mountains, years sometimes elapse without a shower ; a cloud on the sky is regarded as a phenorrJenon ; the rivers are all too insignificant for navigation, and most of them are quite dry during eight months ot the year. A single river of the mountainous region of South America, contributes more water to the ocean than all the rivers of the continent of Africa, which is much more extensive. Even the principal African rivers rise in the highlands under the equator, they receive scarce any accession ot water from the lower dis-tiicts. The part which trees take in the xemoval of electricity from the upper regions, is far greater than might be suspected from their moderate elevation. They increase the quantity of rain and cause it to fall in gentle and seasonable showers, instead of coming in rare and violent torrents. That the destruction of forests is attended with a diminution of rain, is a fact proved beyond doubt from observations made on this continent; and, according to iHumboldt and Boussingalt, the same result is visible in South America. From the result of the experiments of nature, it is evident that by discharging the elec. tricity in the upper part of our atmosphere, we may deprive rain of its injurious effects, and not only render it more beneficial to our wants and to the purposes of agriculture, but even extend those benefits to the sandy deserts and redeem them from their present sterility. The construction of lightning rods on a scale sufficiently large for this purpose, would be attended with the greatest difficulties. A momentary communication with the imprisoned electricity is all that is desirable. A temporary communication may be most readily formed by projecting a considerable body of water into the atmosphere by the means of the expansive force of condensed air, or of carbonic acid subjected to a pressure. The following plan, says Mr. Vaughan, for this purpose seems best calculated to allow the elastic forces sufficient time for action, and to obviate the difficulty of permitting the water to escape at once from an enormous pressure through a large orifice with a sufficient velocity. Let a large tube ot the form of the letter U, or ol a semi-circle, be constructed, and let it be placed with both ends upright and one of them permanently closed. The other end is to be stopped air-tight by means of a large valve, which presses against its mouth, and turns on an axle when opening, while it is secured on the other side by a lever, so arranged that, on the fall of a weight on its remote extremity, ft loses its hold on the valve and allows it to open. At a short distance below this valve, let the tube communicate with a strong vessel, in which carbonic acid is prepared by the action of sulphuric or muriatic acid on carbonate of lime, or with a condenser, if air be employed. Having introduced water in the tube, in a quantity sufficient to fill one-sixth of its capacity, the valve must be closed, and the apparatus arranged for lhe introduction of the air or carbonic acid into the confined space. The gaseous mixture after forcing the water in the closed end of the tube above its former level, will rise through it in bubbles, filling the space over it and attaining nearly the same density as Tn the other end. When the pressure becomes as great as the strength of the tube will permit, the valve being allowed to open, one part of the confined air or gas escapes and clears the orifice for the exit of the water, which is driven into the air by the expansion of the other part of gaseous mixture in the remote extremity of the tube. From a cast-iron tube 200 feet long, 20 inches in diameter, and 2 inches thick, a cylindrical column of water thirty feet long may be in this manner launched into the air, with a velocity of over 700 feet a second and, if not prevented by the air, it should reach an elevation of nearly 8,000 feet. The effect of such a discharge, like the influence of a mountain, must extend to a distance of several leagues; and it Would not be rash to expect that in this manner, the irregularities in the supplies ot rain throughout the habitable globe, may be corrected with much less labor and expense than was bestowed on one of the artificial mountains of Egypt.
This article was originally published with the title "On the Causes of Rain and the Possibility of Modifying them by Art" in Scientific American 8, 21, 168 (February 1853)