Reflection and Refraction of Light. 205 



the original, anci O G the new horizontal motion, hence these are in a 

 constant ratio ; but they are the sines of incidence and refraction to the 

 radius B yl or AD; thus we have a complete and simple explanation, 

 and proof of the law of refraction, and perhaps the first dynamical proof 

 ever given independently of hypothetical principles : and thus the reader 

 has before him a satisfactory solution of the 1st, 2nd, 3rd, 5th, Cth, and 

 8th facts stated in the twelfth article. 



24. Since, according to these principles, the atoms of light difier, both in 

 regard to their absolute force and to their spheres of repulsion, and that 

 evidently an atom will be less refracted as its absolute force is greater, or 

 as its sphere of repulsion is less j it follows, that different sorts of light 

 will be refracted differently, accounting accurately for the prismatic dis- 

 persion of liglit, as in the seventh fact enumerated above, and perhaps this 

 is the only physical explanation which can be given of this curious and 

 important property of light. 



The fourth fact will be a natural consequence of slight irregularities on 

 the surface of the medium, and the pnlses excited at the point of Incidence 

 by the atoms of the beam of light, which will produce, not only scattered 

 radiations at that point, but also the absorption of many atoms which so 

 meet the medium as to have their motions destroyed or altered, by com- 

 municating it to the atoms of the medium. 



25. To explain the ninth fact, let the ray proceed from the denser to 

 the rarer medium, as from DA to A B, fig. 4, hence the preceding rea- 

 soning will shew, that the angle EA Bis always greater than DAG, and 

 becomes a right angle, while this is acute, and at this point the refracted 

 light, if it proceed at all, must pass along the surface of the medium, and 

 at all greater angles of incidence, it must be reflected, and so that the 

 angle of reflection shall be equal to the angle of incidence, and hence 

 total reflection will be the result. 



From what has been advanced, it is manifest that the less the difference 

 between the density of the ethereal matter accumulated on the surfaces of 

 the two media, where they are conjoined, as at FA, the less will be the 

 refractive force, or difference of action at m and n, and consequently the 

 deviation will be less, and will vanish when these are equal, answering to 

 the second fact originally stated. 



The foregoing considerations indicate, that bodies which absorb much 

 light, communicate much heat; since according to this theory caloric is 

 the same as light, except th,it, as caloric, tlie atoms are moving with a less 

 velocity, which here is communicated by the action of tlie liglit absorbed. 



Having thus given the tiirce explanations of the important and funda- 

 mental facts relating to liglit, as proposed, it now remains with the reader 

 to judge and decide for himself respecting the merits of each, and to satisfy 

 himself on the question, which is the most simple, natural, and easy to 

 understand, and most in accordance with dynamical principles. 



No. 4.— Vol. I. 2 E 



