PROPERTIES OF LIGHT, ] ^5 



same angle of incidence, which cannot take place on the Wuh that of 

 hypothesis of Huyghens: for we must necessarily conclude "y*'^"*' 

 from them, not only that light is a substance obedient to the 

 forces that set other substances in action, but also that the 

 form and arrangement of its particles have great influence 

 on the phenomena. 



If we transfer to the luminous particles the three rectan- AH thepheno- 

 gular axes, a, 6, c, to which the phenomena 1 have described ^^^ f^^^^ ^ gi^' 

 are referrible ; and if we suppose, that, the axis a being gle law, 

 still in the direction of the ray, the axis b or c, from the in- 

 fluence of the r^pw/Ai re /joamv, becomes perpendicular to 

 the direction of these powers; then all the phenomena of 

 total reflection, and of partial reflection, and the most ex- 

 traordinary circumstances of double relVaction, become 

 consequences of one another, and are deducible from this 

 single law, namely, that; 



If we consider, in the transference of the luminous parti- The law. 

 cles, their motion round their three principal axes, a, 6, e ; 

 the quantity of particles, the axis & or c of which becomes 

 .perpendicular to the directio'n.of the repulsive forces, will 

 always be proportional to the square of the cosine of the 

 angle, which these lines will have to describe round the 

 axis a, to take this direction; and reciprocally, the quan- 

 quantity of the particles, the axis 6 or c of which will ap« 

 proach the nearest possible to the direction of the repulsive 

 forces, will be proportional to the square of the sine of the 

 angle, which these lines will have to describe in their rota- 

 tion round the axis a, to arrive at the plane, that passes 

 through this axis and the direction of the forces. 



In the case of double refraction, and when we consider the 

 phenomena, that are exhibited by two contiguous crystals, 

 we may express this law in the following manner. 



If we conceive a plane passing through the ordinary ray Law in the 

 and the axis of the flrst crystal, and a second plane passing '^^^ of double 

 through the extraordinary ray and the axis of the second 

 crystal, the quantity of light proceeding from the ordinary 

 refraction of the first, and refracted ordinarily by the second, 

 is proportional to the square of the cosine of the angle com- 

 prised between the two planes abovementioned ; and the 



quantity 



