Page:Popular Science Monthly Volume 45.djvu/508

490 : To cool down the cubic mile of air to the dew point would require the abstraction of as much heat as would raise eighty-eight thousand tons of water from the freezing to the boiling point. To cool it eleven degrees more would require the abstraction of the same quantity of heat again. This would cause the precipitation of twenty thousand tons of water, which, spread over a square mile, would give 1·4 pound per square foot or 0'27 of an inch of rain. The amount of heat which the twenty thousand tons of water vapor would give off to the particles upon which it would condense would raise a hundred thousand tons of water from the freezing to the boiling point, and this would also have to be taken from the air in order to allow the condensation to continue. According to this computation, enough heat would have to be extracted from the air to raise two hundred and seventy-six thousand tons of water from the freezing to the boiling point in order to produce a rainfall of about a quarter of an inch over an area of a square mile. This two hundred and seventy-six thousand tons of water would cover the same area to a depth of more than six inches. Accordingly, in order to produce a rainfall of a quarter of an inch under the conditions mentioned, enough heat would have to be taken from the air to heat a body of water covering the whole area to a depth of ninety feet through one degree Fahrenheit.

To accomplish this purpose Mr. Dyrenforth proceeded to raise the temperature of the air still higher by means of heat-producing explosives.

Under these conditions eight balloons, a hundred and fifty shells, and four thousand pounds of rosellite were fired off. No rain appeared. One balloon exploded within a black rain cloud, but failed to produce any precipitation. On the following Wednesday, with a clear sky, ten balloons, a hundred and seventy-five shells, and five thousand pounds of rosellite were exploded, and the sky remained clear. On the following night the remaining stock of explosives were fired off, regardless of consequences, to get rid of them.

At the time of this national fiasco, another patented plan of rain-making was published, and it was reported that Senator Farwell liked it even better than the concussion plan. It proposes to send up liquefied carbonic acid and to set it free in the portion of air from which it is desired to precipitate the rain. The carbonic acid in vaporizing and expanding must take heat from the surrounding air sufficient to set its molecules vibrating in the gaseous form. Unquestionably we have here the proper kind of an agent for producing rain. The only question to be considered is one of finance. Prof. Macfarlane estimates that one pound of carbonic acid in taking the gaseous form at 72º F. would take up