320 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



centimeters of mercury; in tlie case of particles of 0.00001 centimeter 

 diameter, to 1 or 2 centimeters of mercury, that is, to pressure incre- 

 ments certainly met with in steam jets. The fact that nuclei of a few 

 hundred molecular diameters are needed is the very feature of these 

 experiments, and explains why smoke and other coarse material is use- 

 less, and why the condensation-producing dust must be so highly 

 specialized." Glowing charcoal and red-hot platinum produce effects 

 similar to those of flame, owing, according to Professor Oarus, to the 

 escape of clouds of exceedingly minute particles from these objects. 

 "Dust-stimulated condensation differs merely in degree, not in kind, 

 from jet condensation in air," for air always contains fine dust. "Air 

 nominally purified needs only a higher degree of supersaturation to 

 evoke condensation running through the whole gamut of colors." Mr. 

 Bidwell found the following substances active in the condensation of 

 the jet: Air, oxygen, or nitrogen, in which the electrical discharge was 

 occurring; burning and incandescent substances; fumes from phos- 

 phorus; hydrochloric acid; sulphuric acid vapor; nitric acid vapor; 

 acetic acid vapor. The following were inactive: Air, etc., in which 

 the electric discharge had ceased for about ten seconds; smoke with- 

 out fire; bottled phosphorus fumes; ozone, steam, alcohol vapor; formic 

 acid vapor; sulphurous acid. Finding that the effects of a discharge 

 in nitrogen and in oxygen separately were the same as in air, Mr. 

 Bidwell concluded that the action is due in some way to dissociated 

 atoms of nitrogen and of oxygen. Bobert Helmholtz suggested such 

 an explanation, having discovered that flames and incandescent sub- 

 stances generally cause dissociation of the molecules of the surround- 

 ing air; and Mr. Bidwell hints at the possibility of the necessity of the 

 presence of water, as in so many chemical reactions, to recombine 

 dissociated atoms. 



The whole subject is an important one to meteorology and merits a 

 searching and full investigation. 



The difference of weight in drops after falling through a measured 

 height in different states of the air, dry and moist, and the relation of 

 loss or increase of weight to size of drop. 



The gain or loss in weight of drops similarly let fall, but previously 

 strongly or feebly electrified. These experiments to be tried in satu- 

 rated and in foggy air. 



The increase in weight and bulk of particles and bullets of ice allowed 

 to drop through saturated and foggy air and through misty rain at a 

 low temperature. The ice bullets to be cooled, before falling, down to 

 several degrees below 0° C, and the effect of electrification to be tried. 



Similar experiments to be tried in the laboratory; e. g., frozen spheres 

 of water to be rotated rapidly through freezing fog artificially produced 

 in a closed space; the icy spheres and the fog to be electrified, and the 

 gain in weight of the ice sphere to be noted, also the relation of rapid- 

 ity in rotation and differences of temperature and electric state to the 

 observed increase. 



