362 Prof. Bartlett on Molecular Moticns in Polarized Light. 
having changed not once but twice or thrice, | Although 
Professor McCullogh has shown, in his elaborate treatise on 
crystalline reflexion and refraction, as published in the memoirs 
=«.sin —* (Vt—r) de aorta 
in which the molecular vibrations are parallel to the axis a, and 
the wave propagation in the direction of the plane yz,§ the actual 
molecular displacement at the time f, « its maximum value, J, 
the velocity of wave propagation, + the wave length, andr the 
Pp 
distance of the molecules place of rest from the origin. 
Living force and quantity of motion in a plane polarized wave. 
Differentiate eq. (1), with respect to § and ¢, we find :— 
Denote the density of the medium by 4, and the area of any 
portion of the wave-front by a, then will the mass between two 
consecutive positions of this area be a.4.dr, and the living force 
within a quarter of a wave-length be :— 
r d &2 Vi-—r=0 on on 
A.a.dr aay A.a.—.a2, V2,cos? — (Vt—r) 
Je G48 Tipe + x | 
Qn m2 
Xzdr=t >. V.A.a. V.a?, 
(2) 
sao ¥ 
Dividing by the. volume a. V, and recalling that * and = are 
? 
organs of sense upon which they act. 
