ARTIFICIAL RAINS. 497 



times be an upper stratum of air, containing so much ca- 

 loric that its specific levity would prevent the upmoving 

 column from rising into it far enough to cause rain. 



These three things, I conceive, are the only circumstances 

 which prevent great fires from producing rain at all times 

 when they occur. The first two can be ascertained with- 

 out much difficulty by means of small balloons and the 

 dew point ; the last, in the present state of science, cannot 

 always be known, and a failure on that account must be 

 risked by the experimenter. 1 This risk I am willing to run, 

 if Congress or the State legislature will promise a sufficient 

 reward in case of success. 



It has been objected to my project that I propose too 

 much, and that it is utterly absurd to expect to make it rain 

 in time of drought, when there is such a scarcity of vapor 

 in the air. 



Now, this objection is founded on an entire ignorance of 

 the fact, arising from a want of due consideration. For 

 there is generally more vapor in the time of summer 

 drought, than at any other time, as I know by experiments 

 constantly made almost every day for these last ten years ; 

 and this is reasonable in itself, for the vapor is rising into 

 the air and increasing every day of dry weather, preparing 

 for another rain. A quiet state of the atmosphere is also 

 more likely to occur, to great heights, in time of droughts 

 than at any other time, for immediately after rains there 

 are sure to be cross currents of air, produced by the in- 

 ward motion of the air at the lower part of the cloud, and 

 an outward motion in the upper part, which require some 

 time after the rain to come to rest. 



If I have succeeded in showing that there is any the least 

 ground to hope that an attempt to produce rain, might some- 

 times- succeed under favorable circumstances, and that those 



1 This difficulty will probably be overcome by Pouillet's Actinometer, lately 

 invented. 



63 



