VOL. XXXV.] IHILOSOPHICAL TRANSACTIONS. 301 



ing greater than that of the violet, the same degree of attraction could not give 

 it the same flexure. 



This is confirmed by experiment : for when the lower prism is not pressed 

 hard against the upper, as in fig. 3 1, the rays brought down to r make a spot, 

 of a colour made up chiefly of red and orange rays ; but when the prisms are 

 pressed closer, the spot grows larger, and perfectly white in its middle, because 

 all sorts of rays are brought down to the spot ; but it is inclosed round with a 

 reddish border, occasioned by the parts of the prism which are very near, but 

 not in contact, or at least not near enough to bring down the green, blue, 

 purple and violet rays. This shows that the reflection is not made from the in- 

 terior solid parts of the glass, nor from the parts in the surface, as Rizzetti 

 affirms. But this is made more evident by 



Exper. 8. — A candle being in the position k, fig. 17, the eye at e, and the 

 prism at abc ; a strong image of the candle was seen at k, as in fig. 7. But 

 lifting up a vessel of water vssv, till the surface of the water vv touched ab 

 the lower surface of the prism, the image of the candle became almost insen- 

 sible, as the eye lost all those rays which now were attracted into the water. 

 And for a further proof, that the reflection is made under the surface, and not 

 in it, when the prism was taken out of the water, being wet at its lower sur 

 face, or having a stratum of water, whose surface was vv, fig. 18, under ab, 

 the image of the candle again became vivid, the rays being turned up again 

 under vv. Indeed the image, in this case, though strong, did not appear 

 well defined, by reason of the unevenness of the watery surface vv, fig. 18. 



I am very well aware that Rizzetti may answer here, that what I have said 

 above, does in some measure favour his notions ; and that the rays which, in 

 fig. 7, having passed through ab, the lower surface of the prism, are turned 

 up again to the eye at e, do not suflTer a reflection, but a nevv immersion; for 

 he says, in p. 125, "An English gentleman, (meaning Sir Isaac Newton,) 

 subjoins secondly, that if light, in passing from glass into air, should fall then 

 in an angle of 40 degrees, it is entirely reflected. To which I answer (says 

 Signior R.) that from what I have laid down in Prop. 4, Case 1, Opt. 1, it 

 follows, that this is not a true reflection of the light, but rather a new immer- 

 sion ; and therefore I deny that it follows from that phenomenon, that light is 

 reflected from the solid parts of bodies, at some distance." And a little lower, 

 having quoted what Sir Isaac says, concerning the blue light, which, coming 

 from one prism obliquely on the farther surface of another, is wholly reflected, 

 at the same inclination that the red light is wholly transmitted ; he says, " Let 

 it again suffice to answer, that in this case also, what the author calls a reflec- 

 tion, is a new immersion of the light." 



