336 Dr. Forster on the dispersive Power 



cular band of light which he produced, instead of being di- 

 versified by the various colours, was always quite uniform, and 

 resembled the light of his disk when viewed steadily in the 

 ordinary manner. This discovery of the different results from 

 viewing the planet Mars and the star Lyra in the same man- 

 ner, gave additional interest to the experiment, for it showed 

 that the colours were not the mere effect of the varying in- 

 clination of the glass of the telescope. I then repeated the 

 experiment on other stars, and on the planet Jupiter; the re- 

 sults of which are as follows : 



Lyra produced the blue very strong, and the red, the 

 indigo, the green and the yellow in successively less propor- 

 tions. Spica Virginis showed nearly the same phenomena as 

 Lyra, only the blue was still more preponderating. « Cygni 

 showed a preponderance of indigo, less yellow and blue. 

 Betalgeus produced yellow, and intense red and green. Sirius 

 showed much indigo, violet, and portions of bright white 

 light. Capella much orange, red, green, and less of the more 

 refrangible colour. Aldebaran principally red, with some 

 green and very faint orange. Arcturus produced a much less 

 coloured ring than the others ; indeed its portions seemed to be 

 orange and red running into each other. The planets Jupiter 

 and Mars showed no colours at all ; the rings produced by 

 viewing them with a gyrating telescope, being only circles of 

 light ol the ordinary and uniform colour of those planets 

 respectively. When any identical star was observed, the same 

 colours were always produced in whatever direction I vi- 

 brated the telescope : — thus a horizontal motion produced a 

 horizontal rod or line, one end of which was red, the other 

 blue, the middle green, and so on. 



I trust I have made myself understood, in this short and 

 hasty account of a phenomenon which, — whatever may be its 

 precise cause, or whatever may be the particular hypothesis in 

 chromatics on which we may attempt to explain it, — certainly 

 deserves future attention. For it must strike every body im- 

 mediately, that however easy the explanation of the produc- 

 tion of colours might be on ojitical principles, were the effects 

 uniform, yet the following considerations must add great im- 

 portance and interest to the experiments. 



1 . That the planets do not produce any colour when viewed 

 by this method. 



2. That the light of some fixed stars cannot be very di- 

 stinctly separated by this method into the several colours, 

 particularly Arcturus, 



3. That the colours produced on the above method, seem 

 generally to agree with those obtained by the adaptation of 



the 



