204 



Reflection and Refraction of Light. 



densed j so that the lengths of the pulses will necessarily be inversely as 

 the refractive densities, which also perfectly accords with observation and 

 fact. Hence it follows that when rays of light meet a new medium per- 

 pendicularly, as in fig. 3, some part of them, generally less than half, be- 

 cause the accumulation of ethereal matter is not excessive, will be reflected ; 

 and the azimuth of the transverse pulse, as at Z>, will not at all, in this 

 case, affect the circumstances conducive to reflection or transmission. 



22. Let the attention be now directed to the progress of oblique rays, 

 as B A, fig. 4, draw BE parallel, and EA perpendicular to the surface 

 FA, which suppose horizontal; in the case of reflection it is seen, that as 

 the vertical motion diminishes while the obliquity increases, so the quan- 

 tity of light reflected will on this account continually increase, with the 

 angle of incidence, which actual experiment confirms. Whether the light 

 is reflected or transmitted, it is manifest that it will continue in the plane 

 of incidence, since there is nothing to deflect it from that plane. When 

 the light is reflected the horizontal motion is destroyed by the reaction of 

 the condensed ethereal atoms at the common surface, but this will be 

 exactly restored by the equal action on the other side of the perpendicular, 

 because the ray returns in the same medium, and consequently meets the 

 same disposition of ethereal matter j hence the angles of incidence and 

 reflection will be equal. 



Fig.'U 



23. Next suppose the atom at the new sur- 

 face in such a phase of its pulse that it is 

 transmitted, and let the lower medium be the 

 denser, as represented in fig. 4 ; now when 

 transiting the common surface at A, it is evi- 

 dent that the resistance is greater at n than at 

 m, hence by the reaction of the etiiereal matter 

 at n, a deflection, or kind of reflection, will 

 take place from the direction BAP, to some 

 new direction A D, which will depend on the 

 difference of resistance at m and n, when the 

 atom A, and the angle of incidence are given ; and also on the horizontal 

 velocity B E, when the angle of incidence is variable : hence when the 

 media and the atom A are given, the resistance at n will depend on the 

 horizontal velocity alone, and will be proportional to it ; for whether the 

 deflection be effected at one pulse, or at several, the resistance will depend 

 equally on the same cause for each, and the horizontal velocity will be 

 changed, either at once or at successive intervals, by a quantity propor- 

 tional to itself : but the absolute velocity remains unaltered, on account 

 of the perfect elasticity of the ethereal matter : therefore taking A D equal 

 to A B, and drawing the perpendiculars, B E and D G, to the vertical 

 line J BA and AD will be described in equal times, but B ^represents; 



fjji^ 



