216 PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 



latiiig". But after the tendency to eondensatiou has ceased altogether 

 the changes in the clouded air are not at an end. The smaller drops 

 begin to lose their accumulated moisture, while the larger ones are still 

 growing — growing at the expense of the gradually diminishing smaller 

 ones. This process goes on till most of the small ones have lost all their 

 burden of water, which has been absorbed by the overgrown larger ones : 

 and in the end a comparatively small number of drops have absorbed 

 t-he moisture which was previously distributed over a vast number of 

 particles. The larger particles have, so to speak, eaten up the smaller 

 ones. How like the above looks to a page in the " struggle for exist- 

 ence" in the animal or vegetable world! 



Color pho) omen a in steam jets. — Steam escaping into the atmosphere 

 has been observed on a few occasions to have the power of absorbing 

 certain of the rays of light, and causing the sun, when seen through 

 it, to look "blue" or ''green." Principal Forbes observed colors in the 

 steam escaping from a safety valve. Mr. Lockyer* states that, when 

 on Windermere, he saw the sun of a vivid green, through the steam of 

 a little paddle boat. I believe a few others have seen this phenome- 

 non under similar conditions, but so far as I am aware no one has fol- 

 lowed out the suggestion and "investigated the manner in which the 

 color is produced. 



Mr. Bidwell, in his experiments on the electrification of steam jets, 

 studied the action of the jet on light by casting the shadow of the jet 

 on a white screen, using for illumination the lime light. He found that 

 the shadow of the ordinary jet — that is. the light transmitted by the 

 jet — was nearly colorless, but that when it was electrified the shadow 

 became of a dark orange-brown color. 



The color of the " green sun " seen through steam has been attrib- 

 uted to the absorption of l)oth ends of the spectrum ])y the aqueous 

 vapor. This explaiuition is obviously not the correct one, as it will be 

 found that a moderate length of steam has no percei)tible selective 

 absorption. Through a length of even 1 meter of steam white ol)jects 

 are not colored, and we shall presently see that the coloring dejiends 

 not on the vapor, but on some action of the small drops of water in the 

 condensing steam. 



For the purpose of studying the color plienomeiia of steam jets 1 have 

 found it to be a great advantage to snrrouiul the jet by solid walls. 

 When a jet condenses under ordinary conditions, the constitution of 

 the jet rapidly changes in its passage away from tlie nozzle, owing to 

 the air mixing with it; and it has been found tliat by inclosing tlie jet 

 in a tube, after a certain amount of air has been mixed with tlie steam, 

 that the conditions can be kept fairlv constant for some length of time, 

 and the color i^henomena taking place can therefore be more easily 

 studied under these conditions. The tube used for this purpose need 



Xiilure, .Imic. (i, 1878: vol. xviii, p. 1.55. 



