of the Atmosphere. 1 29 



which it could be viewed. Looking end on from below, the 

 steam-jet caused that part of the heavens obscured by it to appear 

 feebly orange-coloured — the day was bright, but the sky at this 

 quarter was overcast. On looking through the jet of steam fi-om 

 below upwards, but in a direction inclined about 11° to the axis 

 of the jet — in which position a portion only of the steam-cloud 

 could be viewed by the direct light of the clouds, the remaining 

 portion being sheltered by the side of the window — one part of 

 the jet appeared orange-red, namely that part which transmitted 

 the direct light of the clouds, while the other portion was blue. 

 The biueness of the jet increased with the above-mentioned angle 

 until the angle was perhaps 30°, after which the biueness some- 

 what diminished, but was far from being extinguished at 90°. 



193. By partly closing the cock of the boiler, and so dischar- 

 ging steam from the jet of, perhaps, not a higher pressure than 

 10 lbs. on the inch, I could obtain a jet of steam, which, looking 

 end on from below, was blue. It was rather difficult to obtain 

 this blue jet, and when obtained, it kept alternating with violet. 

 On now viewing this blue jet under an angle, as before (192.), 

 of about 20^, it appeared reddish-orange in colour ; this colour 

 was not visible at almost any angle, hke the reflected blue (192.). 



194. Looking end on, and adjusting the pressure, I have 

 occasionally seen for a moment at a time a bright green jet ; also, 

 and commonly, a blue purple. In the reflected tints I am not 

 sure that I have seen anything more than orange-red, violet and 

 blue. The transmitted colour appeared in my experiments more 

 intense than the reflected tints. This, perhaps, has its explana- 

 tion in the fact, that when looking end on, the eye receives light 

 which has shone through a columnar arrangement, whose length 

 is much greater than its diameter, — while the reflected lights 

 could only be seen by looking on the convex surface of the co- 

 lumnar stream of particles. 



195. Prof. Forbes, after discovering the red colour of a jet of 

 steam by transmitted light, connected the red colour of the 

 clouds with this fact ; and the truth of this connexion is beyond 

 dispute. So far, however, as I have been able to go, the colours 

 of the steam-jet are manifestly only instances of ordinary intei*- 

 ferencc, greatly resembling that produced by thin transpai'cnt 

 plates ; the transmitted ray being always complementary to the 

 reflected. Thus in (192.) the transmitted light is red, as in 

 Prof. Forbes's experiments, but the reflected light is blue. It 

 is therefore to be inferred, that all the colours of the clouds ori- 

 ginate in intex'ference, caused by minute drops of water, the size 

 of which determines their colour ; while the blue jet (192.) is, I 

 think, strictly analogous to the bhic sky. 



7 ProsjMjct Place, Ball's Pond lload, 



June 28, 1852. 

 Phil. Mag. S. 4. Vol. 4. No. 23, Aug. 1853. K 



