ATMOSPHERE IN RELATION TO HUMAN LIFi, AND HEALTH. 319 



The effects of mixture of invisible steam of different temperatures, 

 of visible steam at different temperatures, and of each of these in dif- 

 ferent electrical states. The growth of size, and the color, of the steam 

 particles and the effects of absence and presence of much dust or 

 smoke. 



The true results of the electrification of jets of steam or cloudy 

 masses, the relation of the size of the deposited vapor particles to the 

 electrification, and the optical effects of various degrees of electrifica- 

 tion in air. 



The effect of an electric field on the surface tension of drops of water, 

 and the various effects of varying amounts and proximity of the elec- 

 tricity of the charged surface on drops of different sizes. When the 

 electrical field is uniform the surface tension of the drop is only slightly 

 diminished, and the diminution is independent of the size of the drop. 

 Very small drops thus preserve their high surface tension in the 

 neighborhood of an electric field. But when there are a number of 

 charged atoms surrounding the droplets the effect is different; the 

 diminution of surface tension which is brought about varies inversely 

 as the square of the radius of the droplet. The whole subject of the 

 electrification of gases, dry and moist, the electrification of drops of 

 water and their behavior under electrification, and the relation of sur- 

 face tension in cloud globules and drops to electricity in natural condi- 

 tions, requires investigation. The "cloudy condensation" of'steam, 

 and the optical effects in electrified steam have hitherto led to conflict- 

 ing inferences, and careful observation has not yet proved a diminution 

 or increase in the size of the water particles or a recombination of dis- 

 sociated molecules of oxygen and nitrogen. The question is of great 

 interest in many respects, and may have a bearing on thunderstorms, 

 rainfall, evaporation, and chemical problems. 



Shortly stated, there are three principal views of the apparent 

 action of electricity on steam. Mr. Aitken believes that the thick con- 

 densation, coloration, etc., of a jet of electrified steam is due to the 

 prevention of the coalescence of the very small condensed particles 

 which would occur without electrification. Mr. Bid well believed that 

 the effects were produced by the conglomeration under electric excite- 

 ment of particles which would otherwise have evaporated unseen, not 

 becoming large enough to cause visible obstruction of light. These 

 views are related to Lord Kayleigh's discoveries on the behavior of 

 drops under electrification; the drops coalesced when weakly, and 

 repelled each other when strongly electrified. 



Prof. Paul Carus holds a very different view, and considers that the 

 condensation effects depend on the action on steam of exceedingly 

 small particles of dust. "One may estimate," he says, "that pure 

 dust-free, uncoufined steam at 100° would require a pressure of 10 

 or more atmospheres to condense it. Add to this dust particles less 

 than 0.000001 centimeter in diameter, and the pressure sinks to 15 



