28 Dr. J. Reade on a new Theory of Telescopes. 



from these two pieces of cloth, and rarefied by sticking on the 

 pane. The violet is evidently compounded of the orange 

 blending with the black light of the lower piece of cloth, and 

 the reader is to notice that when these two pieces are kept 

 asunder, we never perceive more than four colours, — blue, red, 

 yellow and violet : but if we now direct an assistant to approxi- 

 mate the pieces, the yellow fringe of the upper one imme- 

 diately passes over the blue fringe of the lower piece, and 

 forms a vivid green ; and until this takes place, no green is 

 ever formed. The rationale of this interesting experiment is 

 too obvious to require much observation. The square piece 

 of black cloth represents the dark window-shutter of Sir Isaac 

 Newton's experiment ; and the two semicircular cuts, when 

 united, represent the circular hole through which the sun- 

 beams passed. The black light reflected from the edges of 

 the hole was rarefied by striking the plane of the prism into 

 colours, and mixing gave the spectrum of seven colours to the 

 eve. 



Here we have to remark, that the light passing through 

 the centre of this hole was colourless, not mixing with the 

 fringes, entirely produced by rarefied black light, as is easily 

 shown by passing the shadow of a knitting-needle through a 

 prbm placed in the sunbeams. Here we are also to remark, 

 that the green is formed alter emergence by a mixture of the 

 blue and yellow, and by no means a simple colour as Newton 

 supposed. Thus did Sir Isaac Newton compound what he 

 calls seven with the three simple and primary colours, — blue, 

 red, and yellow. I am fully confident that no unprejudiced 

 person, alter repeating this easy experiment, can for one mq^ 

 ment doubt that this great philosopher was entirely mistaken 

 in his inference; and however we may admire the ingenuity 

 of that reasoning, which for centuries could make the world 

 believe that transparent light was a compound of opaque rays, 

 yet we cannot extend our approbation to those gentlemen, 

 however learned or respectable, who in the face of direct ex- 

 periment, and I will venture to say common sense, continue 

 to uphold false principles. If the experiments I have pub- 

 lished can be refuted, I am ready to give them up and Ac- 

 knowledge myself in error; if not, I call on those gentlemen to 

 act with candour and liberality, 



I now varied this experiment in the following manner: I 

 allowed the sunbeams to pass through the hole, and placing a 

 prism behind it, so as to pass them through the lower refract- 

 ing angle, I perceived a beautiful oblong spectrum of the hole, 

 not the sun, on the opposite wall : that this spectrum was ob- 

 long and not circular, by no means surprised me, as I had al- 



ready 



