324 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



that this inflexibility is in the inverse sense of the other: which it was besides 

 natural enough to expect. 



Another question may be: Do the principles which explain reflexion, explain 

 flexion ?* To answer this question, there are 2 indispensable preliminaries: to 

 recount the principles laid down for explaining reflexion; and to show with preci- 

 sion the laws of flexion. The principles admitted above are, 1. The repulsive 

 force acting according to a direction perpendicular to the reflecting surface. 2. 

 The red ray more repulsive than the violet; or, in general, the least refrangible 

 rays more forcibly repelled than those that are more refrangible. 



The laws of flexion, very well determined by Mr. B., may be thus stated : 1 . 

 The most inflexible ray is also the most deflexible. 2. The most refrangible ray is 

 the least flexible. Thus, the red ray is at once more inflected, and more de- 

 flected, than the violet, in the same circumstances. The law of deflexion follows 

 well from principles in what concerns this phenomenon alone. The red rays de- 

 monstrate here, as in reflexion, their greater force of repulsion. As to the law of 

 inflexion, it does not follow from the principles which explain reflexion. We may 

 say, that the most repulsive rays are also the most attractive. This prop, is ad- 

 mitted by Mr. B.; but the diverse refrangibility of the rays gives a quite contrary 

 indication. 



A 2d question is this: Are the principles acknowledged for reflexion reconcileable 

 with those for refraction ? Mr. P. replies yes: Since the rays have traversed the re- 

 pulsive sphere, they enter the attractive : the red rays are indeed the most repulsive, 

 but nothing hinders the violet from being the most attractive. We may indeed 

 say, that these 2 facts are naturally connected, and that there is reason to expect 

 that the rays least easy to repulse are most easy to attract. Now refraction shows 

 them such : For, 1 . Nothing is better proved in theoretic optics, than the prop, 

 which establishes, that refraction is produced by an attraction perpendicular to the 

 attracting surface. 2. Therefore also, the differences of refraction, and in par- 

 ticular the greater refrangibility of the violet rays, are produced by the same 

 cause: a consequence confirmed by their superior reflexibility in the denser medium. 



A 3d question is this: Can the principles of refraction explain those of re- 

 flexion? Mr. P. says no: the law of inflexion remains unexplained. In this law, 

 the red rays seem the more attractive, while in refraction it is the contrary. " Are 

 not the rays of light reflected, refracted, and inflected, by one and the same force, 

 which displays itself differently in different circumstances ?" Such is the question 

 which Newton made at the beginning of this century, and which seems not yet to 

 be resolved towards the end of it. It is true, that Mr. B. concludes that, " the 

 rays of light are reflected, refracted, inflected, and deflected, by one and the same 

 power, variously exerted in different circumstances." This is, says Mr. P., doubt- 

 less very probable, but not yet proved. 



• Mr. B. very properly names flexion, what most philosophers hare hitherto called inflexion, and 

 some others diffraction. And he distinguishes it into inflexion and* deflexion : the former inclining the 

 ray to the fleeting body, and the 2d bending the ray from it. — Orig * 



