PHENOMENA CONNECTED WITH CLOUDY CONDENSATION, 217 



not be of any special size. For a iet from a nozzle of 1 millimeter bore 

 a tube of 7 or 8 centimeters diameter and abont half a meter Ion"- does 

 very well, but a smaller and shorter tube nuiy be used. With the 

 larger size of tube it may be necessary to check the current through it. 

 Tliis is best done by ]daring a piece of glass near the exit end of the 

 tube, the opening between the glass and the end of the tube being reg- 

 ulated to tlie required amount by observation. When a small jet of 

 steam is used with the large tube open at both ends too much air is 

 drawn in and the effect is nmch the same as if no tube were used. The 

 end of the tube has, therefore, to be closed to a certain extent, to pro- 

 duce the color phenomena. But when high-pressed steam is used, no 

 check on the circulation through the tube is necessary. The steam 

 nozzle should be placed outside the tube and a little to one side, so that 

 the eye can be brought into a line with the axis of the tube and a clear 

 field of view obtained while the jet inlays into the open end of the tube. 

 This is an experiment which well repays the trouble of making it. 

 When the amount of steam, dust, and other conditions are properly 

 proportioned, the colors seen are very beautiful. With ordinary con- 

 densation the color varies from a fine green to lovely blues of different 

 depths. The pale blues equal any sky blue, while the deeper blues are 

 finer than the dark blues seen in the sky, as they have none of the cold 

 hardness of the dark sky blues, but have a peculiar softness and full- 

 ness of color. 



Suppose now the tube is fitted up pointing to a clouded sky, or 

 other source of light, and that the steam jet, under slight pressure, is 

 blowing through it. If tlie exit end of the tube be open we shall see 

 very little color, and what is seen is only near the origin of the jet. If 

 now we partially close the end of the tube with the glass plate, to pre- 

 vent the jet drawing in so much air, we shall find that color begins to 

 appear, and that Avhen the plate is properly adjusted the tube looks as 

 if tilled with a transparent colored gas. Tlie first decided color to 

 ai)pear is generally green, though I think I have frequently seen a pale 

 crimson before the green was visible. If circulation be checked still 

 further, the color will change to blue of a greater or less depth, accord- 

 ing to the conditions. 



The above are the effects which may be looked for when the conden- 

 sation of the jet is ordinary; but suppose it be now caused to change 

 to the dense form, then the color seen through the tube also changes. 

 If, when the jet is condensing in the ordinary way, and the transmitted 

 liglit is green, we cause the condensation to cliange to dense, then the 

 color also changes and becomes deep bhie, or, if the ordinary conden- 

 sation gave blue, the color changes, when the jet is dense, to a dark 

 yellowish-brown. But between the blue and the yellow there is always 

 an intermediate stage when . all color disappears and the light is sim- 

 ply very much darkened. The most common effect of the change of 

 the condensation from ordinary to dense is for the transmitted light to 



