Re/lection and Refraction of Light. 203 



Physical Optics : it may be here observed, that according to the Newtonian 

 theory the velocity of light is greater, and according to the Huygenian 

 theory it is in the same degree less, in dense than in rare media. 

 ^'s-'^- 21. Since the absolute force of an ethereal 



p^p atom is very small, and its velocity in the state 



♦» !!,li ^M.o ^^ ^'n'l' is very great, and that the ethereal 



Q^^ *^^k& matter of the medium will be urged within its 



»n'' ' ' ^s sphere of repulsion near the centre, both before 



&vt'-<v|P ^-v::^v-::-::?^v-::-:-y-; ^^^ behind, it is manifest that the pulses will 

 ^^^v>ri^^*'*^''^*^^B"""** ^^ extremely short ; but that still they will be 

 ^^ 5:/lM different for the different sorts of light, since 



^^^ their lengths will be greater as the absolute 



force of the moving atom is greater, and as the sphere of its repulsion is 

 less ; and thus we are furnished with a natural and easy view of the New- 

 tonian fits, which correspond with the waves in the undulatory theory. 

 The length of the pulse is the distance between two similar points, in con- 

 secutive pulses. The pulse thus excited, which may be called the direct 

 pulse, will produce others, by the displacement of the ether : particularly 

 a pulse will arise perpendicular to the path, as at D, fig. 3, and this after 

 having acquired any particular azimuth, considering D B as a vertical line, 

 will retain that azimuth while the medium remains uniform ; since all 

 its deviations will, in this case, be compensated : this may be called the 

 transverse pulse ; another, or complementary pulse of small amount, will 

 result at right angles to both the former 5 all other displacements in the 

 ethereal matter will be too slight to require notice. 



The angles, edges, and surfaces of bodies contain an accumulation of 

 ethereal matter, as is shown in the New Theory, and in this respect there 

 will be a difference according to the nature of the body, so that generally, 

 the accumulation of ethereal matter will be more dense at the one surface 

 than at the other in two contiguous media : thus in the figure the ethereal 

 matter at the surface of the lower body is represented as more dense than 

 that at the surface of the upper medium. Now when the atom of light 

 encounters this common surface, as at ^ or R, it will be in a state to be 

 more easily reflected, or transmitted, according to its phase at that mo- 

 ment, which is precisely agreeable to Newton's conclusions : also the less 

 the difference in the accumulations of ethereal matter on the two surfaces, 

 the less will the state of the light be changed, the deviations at one surface 

 being more nearly compensated at the other, so that the light will enter 

 the new medium in greater quantity, and with less deviation j all of which 

 answers perfectly to what occurs in nature. The velocity in every case 

 will remain the same, since every deviation is a sort of reflection, and tiie 

 motion, destroyed in any direction, is always regenerated in the returning 

 direction. Besides, a small degree of attention will shew that the direct 

 pulses must be longer in a medium where the ethereal matter is less con- 



