T 



Doctor Tenney, on PmmaUch Colours. 41 



4. 



second appearance above mentioned, and its -unifonnity in 

 all experiments, on this supposition; yet, if granted, it will 

 answer all the purposes of my argument : for this dispersion 

 of rays, however occasioned, whether *by a different refran- 

 gibility in rays of the same colour, or by the imperfection 

 of the prism, will occasion an intermixture of neighbouring, 

 simple colours; from which the same compound colours 



r ^^ 



must j)roceed, that are produced by the ^ame mixtures in 

 bodies, with which we are more intimately acquainted. 



I know not with what force these reasonings will strike 

 those, who are not influenced by the partiahty which a man 

 commonly feels for his own ideas; but to me, they appear 

 sufficient to warrant a modest conviction, that the original 

 colours, or those inherent in the rays of light, ought to be 

 reduced to these four, Red, Yellow, Blue, and Violet; and 

 that the other three. Orange, Green, and Purple, though 

 among the most pleasing colours, should be degraded from 

 the rank, which they have long unjustly held ; and considered 

 as only some of the most simple of those, that are formed 



by composition. 



After all, Sir, I am sensible it will be said, that in such 

 enquiries, experiment is the only test of truth. It happens 

 rather unfortunately for me, that, if I am right in my princi- 

 ple, that rays of the same colour possess different degrees of 

 refrangibility, the case hardly admits of an experiment which 

 can be decisive. On the other hand, if what I impute to 

 this cause arise entirely from the imperfection of the ^prism, 

 a second prism, so placed as to take only one of those colours, 

 which I esteem compound, might determine the point. For 

 instance, if orange be an original colour, the second prism 



V 



s 



F 



Cl 



could 



