76 DISSERTATION SECOIS1). [part n. 



to compute the thickness of the plates of air, which corres- 

 ponded to the different rings. 



An inch heing divided into 178000 parts, the distance of 

 the lenses for the first series, or for the luminous rings, was 



' 5 , &C. 



178UOO 178000 178000' 



>2 4 



For the second series — — - — ■' t ^ nnnn > &c. 



1/8000 178000' 



When the rings were examined by looking through the 

 lenses in the opposite direction, the central spot appeared 

 white, and, in other rings, red was opposite to blue, yellow 

 to violet, and green to a compound of red and violet ; the 

 colours formed by the transmitted and the reflected light 

 being, what is now called, complementary, or nearly so, of 

 one another; that is, such as when mixed produce white. 



When the fluid between the glasses was different from air, 

 as when it was water, the succession of rings was the same ; 

 the only difference was, that the rings themselves were nar- 

 rower. 



When experiments on thin plates were made in such a 

 way that the plate was of a denser body than the surround- 

 ing medium, as in the case of soap-bubbles, the same pheno- 

 mena were observed to take place. These phenomena 

 Newton also examined with his accustomed accuracy, and 

 even bestowed particular care on having the soap-bubbles as 

 perfect and durable as their frail structure would admit. In 

 the eye of philosophy no toy is despicable, and no occupa- 

 tion frivolous, that can assist in the discovery of truth. 



To the different degrees of tenuity, then, in transparent 

 substances, there seemed to be attached the powers of sepa- 

 rating particular colours from the mass of light, and of render- 

 ing them visible sometimes by reflection, and, in other cases, 

 by transmission. As there is reason to think, then, that the 



