VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. 735 



We are now to see to what conclusions these experimeiUs lead us. — The first 

 experiment shows, that all sorts of light, whether direct, or reflected, or refrac- 

 ted, produces colours by reflection from a curve surface. Fronfi the 2d we learn, 

 that these colours are distinct images or spectra of the luminous body, much 

 dilated in length, but not at all in breadth ; and that the angle of incidence 

 being changed, the dilatation of the images is also changed : and from the 3d 

 experiment it appears, that each full image is composed of 7 colours ; red, 

 orange, yellow, green, blue, indigo, and violet ; and that the proper order is red 

 outermost, and violet innermost, the rest being in their order. The 4th expe- 

 riment shows, that these images are produced, not by any accidental or new 

 modification impressed on the rays, but by the white light being decomposed by 

 reflection ; that the mean rays, or those at the confine of the green and blue, 

 are reflected at an angle equal to that of incidence, and the red at a less, the 

 violet at a greater angle. Experiments 3th and 6th prove, beyond a doubt, the 

 decomposition and separation of the rays by reflection ; for in both we see that 

 the colours in the images are those, and those only, which were mixed in the 

 ray by reflection or refraction, before and at incidence, while the 6th is, in ad- 

 dition, a proof that all the rays of any one image, if mixed together, compound 

 a beam exactly similar to the beam that was at first decompounded. The 7 th 

 experiment shows, that the colours into which the rays are separated by reflec- 

 tion are homogeneous and unchangeable ; that they differ in flexibility and re- 

 frangibility ; that they bear the same part in forming images by reflection, and 

 fringes by flexion, and colours from thin plates, which the rays separated by the 

 prism do: and in the 8th experiment we see, that when the rays are placed in 

 the same situation with respect to refraction, whether out of a rarer into a denser 

 or a denser into a rarer medium, in which they before were with respect to re- 

 flection, the position of the colours produced is diametrically opposite in the 

 two cases. Seeing then that in all sorts of light, direct, refracted, reflected, simple, 

 and homogeneous, or heterogeneous and compounded, and in whatever way the 

 separation and mixture may have been made, some of the rays at equal or the 

 same incidences are constantly reflected nearer the perpendicular than the mean 

 rays, and others not so near ; and seeing that by such reflection the compound 

 ray, of whatever kind, is separated into parts so simple that they can never more 

 be changed ; and considering the different places to which these parts are re- 

 flected ; it is evident, that the sun's light consists of parts different in reflexibility, 

 and that those which are least refrangible are most reflexible. By reflexibility, 

 I here mean a disposition to be reflected near to the perpendicular in any degree. 



Though I have given what I take to be suffic'ent proof of this property of 

 light, yet I am aware that something more is requisite. It will be asked, why 

 does neither a plain, a common convex, nor a common concave mirror separate 



