VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 413 



their eyes on that subject. In the course of those experiments, he had taken 

 notice of something remarkable with regard to colours. Mr. Gray succeeded, 

 and having opened a new path, made still further discoveries in electricity : he 

 likewise, in giving an account of what he had observed, hinted at something 

 curious with regard to colours. But neither of them appear to have come to 

 any determined point in this matter. Mons. Du Fay, who concurred with Mr. 

 Gray, in carrying on electrical discoveries, with a candour and ingenuity that 

 did honour to them both, having entered on an inquiry to determine what sort 

 of bodies were most susceptible of electricity, thought proper, in consequence 

 of what had fallen from Mr. Hauksbee and Mr. Gray, to examine what effect 

 the different colours had in augmenting or diminishing the electricity of different 

 substances. 



Accordingly he ranged a number of ribbands, of all the primitive colours, 

 hanging them in the same vertical plane ; and to these he applied an excited 

 glass tube, in a horizontal direction. On this he observed, that the black was 

 first attracted ; and, as he brought the tube nearer, the white next ; and the 

 rest successively, though not always in the same order. He made another ex- 

 periment, in the same view, with gauzes of different colours, through which 

 he tried the force of an excited tube, on light bodies placed at a proper distance 

 behind them : and from the result he was of opinion, there was something in 

 the influence of colours. But having afterwards tried some experiments with 

 the coloured rays of the sun as refracted by a prism, with flowers of different 

 colours, and with white ribbands rubbed over with differently coloured sub- 

 stances, he began to change his opinion. He likewise had recourse to what he 

 calls a decisive experiment : he dipped his different coloured ribbands in water ; 

 and when they were all equally wetted, he applied his tube, and found they were 

 all equally attracted. From this last-mentioned experiment, in particular, he 

 concluded that colours, as colours, had no effect in electricity ; but that aU was 

 owing to the ingredients of the dye imbibed by the coloured body. 



It is not Mr. S.'s purpose here to inquire, whether Mons. Du Fay's conclu- 

 sion is well or ill founded. Whatever may be the decision of that point, he 

 apprehends the whole of this affair has very little concern with the subject of 

 these papers, and could have been of little use to Mr. S. had he been acquainted 

 with it before. 



Paper IV. Part I. 

 Of Two Distinct Powers in Electricity. 



With regard to positive and negative electricity, Mr. S.'s notion is, that the 

 operations of electricity do not depend on one single positive power, according 

 to the opinion generally received ; but on two distinct, positive, and active 



