The Author’s Conclusions. 59 
rain? A. Floating particles of spongy texture will absorb the 
moisture hygroscopically. If the air is dry this will make it 
drier and prevent rain. If the air is very moist and near satu- 
ration, any solid particles in the air will facilitate the condensa- 
tion; witness the experiments of Aitken and Barus. Thus, 
when other conditions are very favorable, an addition of much 
dust or smoke to the air might determine a fall of rain. 
Q. Will the expansion of carbon anhydride produce rain? 
A. Mr Gathman says he has tried it and with success. LExperi- 
ments should be made systematically. 
Q. Will electric connection with a cloud aid in rain forma- 
tion? A. M Baudouin says it does. 
Q. Will a conflagration produce rain? <A. Quite probably, 
under favorable circumstances. It acts in the line in which nature 
acts, according to the best of our knowledge. Condensation is 
the result of chilling the air. The theory of chilling by mixture, 
the Huttonian theory, a century old, is now known to be ineffi- 
cient. The chilling in nature seems to be due either to the ascent 
of air and its consequent expansion and loss of heat or the chill- 
ing of one cloud by having the shadow of a higher cloud fall on 
it in sunlight. The chilling by ascent-is the method evoked in 
the Espy plan and appears to be by all odds the most effective 
rain-producer in nature. 
Q. If rain can be made, how much will it cost? A. This 
is truly an American question, and quite appropriate to the 
fin-de-siecle. Mr Powers, who, by the way, says that Mr Dyren- 
forth did not after all really try his experiment, puts the cost of 
one experiment with government aid at $80,000. Gathman says 
he can sprinkle the earth at a cost of from $50 to $90 a square 
mile. Espy proposed to fire the low forest growths at regular 
intervals at a cost less than five mills per citizen per year. The 
method of concussion costs the comfort and peace of all within 
hearing, a cost which a much more certain result would not 
justify. 
9—Nat. Geog. Maa., von. VI, 1894. 
