98 Mr. Cooper on the Colours that enter into the 



not only the red, but, also, the green and the violet images, 

 may be seen of this form, quite separated from each other, 

 and without the appearance of any intermediate light. I 

 have not yet seen the three images together by this method, 

 but the green and red, and the violet and red, may be made 

 to appear at the same time, without difficulty. 



In making these experiments, it will be observed that the 

 red image assumes its circular form in consecpaence of the 

 absorbtion of another red image immediately above it ; this 

 red image, which is removed with great facility by means 

 of blue glass, is, probably, formed by the red light after 

 three reflexions. 



Now, all these circular images of the sun, in both methods 

 of making the experiments, must be formed of homogeneous 

 light. What then becomes of the innumerable other circles 

 formed by the intermediate rays 1 Surely it will not be 

 said that these are absorbed, leaving only one of each colour. 

 I will not attempt to answer such an objection, because I 

 do not think it will be made ; and, as I see no other that 

 can be made, the conclusion, that there are only three 

 colours, and three degrees of refrangibility, appears to me 

 to be obvious. 



Upon the same principle, and by the same means, that 

 circular bodies, when seen through a prism, produce as 

 many round images as there are homogeneous rays, correct 

 images of the different forms of other bodies may be pro- 

 duced ; and the number of these images depends, in like 

 manner, on the number of homogeneous rays which they 

 emit, or by which they are illuminated. 



If we look through a prism, held vertically, at the flame 

 of a candle, it produces a spectrum, which increases in 

 length by increasing the distance of the prism ; and if, 

 when at a sufficient distance, we interpose coloured glasses, 

 we may obtain images of the flame of the candle, which in 

 every respect, except in colour, correspond with the original, 

 and with each other, in red, green, and violet light. I do 

 not recollect producing the three images together, but they 

 may be produced either separately, or in pairs, with the 

 greatest facility, and with perfect correctness ; the wick of 

 the candle, and every circumstance attending it, being as 

 distinct as in white light, when viewed by the eye without 

 the prism. 



