424 



Mr. J. Aitken. On some Phenomena [Apr. 28, 



Colour Phenomena 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 colours in the steam escaping 

 from a safety valve. Mr. Lockyer* states that, when on Winder- 

 mere, he saw the sun of a vivid green, through the steam of a little 

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

 under similar conditions, but so far as I am aware no one has followed 

 out the suggestion, and investigated the manner in which the colour 

 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 trans- 

 mitted by the jet — was nearly colourless, but that when it was elec- 

 trified the shadow became of a dark orange-brown colour. 



The colour of the " green sun " seen through steam has been 

 attributed to the absorption of both ends of the spectrum by the 

 aqueous vapour. This explanation is obviously not the correct one? 

 as it wil} be found that a moderate length of steam has no per- 

 ceptible selective absorption. Through a length of even one metre 

 of steam, white objects are not coloured, and we shall presently see 

 that the colouring depends not on the vapour, but on some action of 

 the small drops of water in the condensing steam. 



For the purpose of studying the colour phenomena of steam jets I 

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

 When a jet condenses under ordinary conditions, the constitution of 

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

 the air mixing with it ; and it has been found that by enclosing the 

 jet in a tube, after a certain amount of air has been mixed with the 

 steam, that the conditions can be kept fairly constant for some 

 length of time, and the colour phenomena taking place can, there- 

 fore, be more easily studied under these conditions. The tube used 

 for this purpose need not be of any special size. For a jet from a 

 nozzle of 1 mm. bore a tube of 7 or 8 cm. diameter, and about half a 

 metre long, does very well, but a smaller and shorter tube may be 

 used. With the larger size of tube it may be necessary to check the 

 current through it. This is best done by placing a piece of glass 

 near the exit end of the tube, the opening between the glass and 

 the end of the tube being regulated to the required amount by ob- 

 servation. When a small jet of steam is used with the large tube 



' Nature,' vol. 18, p. 155. 



