Prof. Bartlett on Molecular Motions in Polarized Tight. 363 
Again, the quantity of motion in this quarter of wave-length 
will be :— 
= Whi-r=) 
[radar TRS A.a.@. Vicee=2 (Vise) dbsinca.e, V. (3.) 
retn FE oS Vi-pada A a 
Resolution of living force and of motion, by deviating surfaces. 
Take the co-ordinate plane az in the plane of incidence, and 
the axis z in the direction of the normal to the incident wave, 
the axis y will be parallel to the line of the nodes of the molecu- 
lar orbit in the deviating surface, at the place of incidence, 
Then denoting any portion of the trace of the plane of incidence 
on the denoting surface by s, and the angle of incidence and of 
Teflection by » and ¢’, respectively, will the element of the devi- 
ating surface at the place of incidence be ds.dy, and its projec- 
tions upon the incident, reflected, and refracted wave-fronts, 
Tespectively, be ds.dy.cosy, ds.dycos@, and ds.dy.cos¢’. 
These will take the place of @ in Equations (2) and (8), in com- 
puting the living force and quantity of motion in the incident, 
Teflected and refracted waves. : ; 
Now take a wave of common light and replace it by its two 
Components, having the vibrations in the one parallel and in the 
Tespectively. The living force in the incident, must be equal to 
the sum of the living forces in the reflected and refracted com- 
_ Ponents; whence, equation (2), omitting the common factors, 
ea 
4.cosp. V.a2,-+-A .cosg’. V,.@?2,—A.cos@. V.a2,;=0; 
‘ V ssin 
or, recalling that Pee ’ 
4 i 
A, cosy’ CNG ga, bt, 0 Pv Ab) 
a2 
in which A and A, are the densities of the medium of incidence 
and of intromittance. s) 
€ molecular motions are all parallel to the “ne of os 
and at the same time normal to the directions of t es _ 
Wave motions; they, therefore, make with one another ang - 
equal to those made by the directions of these latter motions, an 
in obtain two more a 
in, Composition of oblique forces. ti 
ction of the motion in the incident wit 
Motions in the reflected and refracted waves, a 
360°~(p—9’), respectively ; and the angles un 
re 180°—2¢9 and 
der which the 
