PHYSICAL PAPERS. 



I. 



Observations on Prismaiick Colours, 



Doctor SAMUEL 



TENNE Y, of Exeter, f. a. a. 



Exeter, 24tli March, 1791. 



Dear Sie, 



HAVE long entertained some doubts of the accuracy of 



S 



Isaac Newton's theory of colours: and 



NuUins 



Jurare in verha rrmgistnl* is the general motto of 

 modern enquirers after truth, I hope, that a modest attempt 

 to point out an errour in it, accompanied with a sincere 

 wish to have mj own opinion rectified, if it 



should 



appear 



of disrespect 



so 



to be wrong, will not be esteemed 

 great a name* 



The part of Sir Isaac's theory, with which I am dissatis- 

 fied, is the number of colours inherent in the rays of light. 

 That a 



into se^ 



a pencil of rays is uniformly separated by the prism^ 

 seven portions, exhibiting each a different colour, is evi- 

 dent to the sight; and that all other colours are made up 



of different combinat 



of these, follows of 



That 



J 



some of the prismatick colours are also mere compounds, 

 I shall endeavour to prove. ' 



The justness of Sir Isaac's Rules of 'phUosopUzing has never, 

 to my Imowledge, been called in question. One of these 

 directs us to "admit no more causes of any phenomenon 

 than are necessary for explaining it": — and another asserts, 



that 



