VOL. VII.] PHILOSOPHICAL TRANSACTIONS. 727 



And as I have given some attention to that subject, and also made experiments, 

 I shall here inform you of what has occurred to me on that new doctrine. 



It seems very extraordinary that the learned author should make light to con- 

 sist of an almost infinite number of rays, endued with a natural disposition of 

 retaining and exhibiting their own proper colours, and that are disposed in a 

 certain peculiar way to be refracted, some in a greater, and others in a less de- 

 gree : that these rays which, wliile promiscuously blended together in open 

 daylight, are undiscernible, and exhibit only the colour of whiteness, should 

 notwithstanding in refraction have rays of one colour separated from those of all 

 others, and, thus separated, appear in their proper and native colours: and that 

 bodies should appear of a certain colour, red for instance, which are adapted to 

 reflect or transmit rays of that colour only. 



This extraordinary hypothesis, which, as he observes, overturns the very 

 basis of dioptrics, and renders useless the practice hitherto known, is founded 

 entirely on the experiment of the prism, in which rays entering into a dark 

 room through a hole in the window-shutter, and then falling on the wall, or 

 received on a paper, did not form a round figure, as he expected according to 

 the received rules of refraction, but appeared extended into an oblong form : 

 whence he concluded, that this oblong figure was owing to the different refran- 

 gibility of the rays of light. 



But it appears to me that, according to the common and received laws of 

 dioptrics, the figure ought to be, not round but oblong. For since the rays 

 proceeding from the opposite parts of the sun's disk are variously inclined in 

 their passage to the prism, they ought also to be variously refracted; that since 

 the inclination of some rays is at least 30' more than that of others, their re- 

 fraction must also be greater. Therefore the opposite rays, emerging from the 

 other surface of the prism, become more diverging, than if they had proceeded 

 without any refraction, or at least with an equal one. Now that refraction of 

 the rays is made only towards those parts, which may be supposed to be in the 

 planes perpendicular to the axis of the prism ; for there is no inequality of re- 

 fraction towards those parts which are conceived to be in planes parallel to the 

 axis, as may easily be demonstrated: for the two surfaces of the prism may be 



was author of several ingenious works, which are written in a manner remarkably neat and clear; by 

 which he acquired considerable credit, and by his talent as a teacher j but, unfortunately for him, lost 

 himself by the above imprudent attack on Sir I. Newton's tlieory of light and colours. His works 

 were chiefly, 1. Elements of Geometry, translated into English by Dr. John Harris, secretary of the 

 Royal Society. 2. Discourse on the Knowledge of Beasts. 3. Statics, or the Science of Moving 

 Forces. 4 Two machines for drawing dials. 5. Discourse on Local Motion. 6. Horologium Tbau- 

 manticum Duplex. 7. Dissertation on the Nature and Motion of Comets. 



