REFLEXION OF POLARIZED LIGHT. 249 
In the system of emission these two angles have no 
“necessary dependence; the contrary is the case if the 
luminous rays are sets of waves, and the relation which, 
in setting out from this hypothesis, one of our most dis- 
tinguished colleagues has deduced from his scientific 
analysis is precisely that which experience has fur- 
nished. Such an accordance between calculation and 
observation ought at the present day to take its place 
among the most forcible arguments which we can pro- 
duce on which to support the system of vibrations. 
m— mI 
vw = aw (1.) 
and m/ receives a velocity 
2m 
{= . 
i ( m—+-m! @.) 
It is also asswmed that this analogy may be applied to a mass of 
zether (m) in vibration outside the reflecting surface, and communi- 
cating its vibrations partly to another mass (m/) at rest within the 
medium; these masses are dependent on and partly retaining it in . 
reflexion. Dependent on the densities, in two contiguous media, and 
the inclination of the ray. 
At a perpendicular incidence the two masses are simply proportional 
m i 
an ; 
this case the velocity of the orm ray being taken as unity, that of 
to the densities or of the refractive powers; or hence in 
the reflected ray will be oF yi and according to the principle of 
vis viva the intensity will be proportional to the square of this quantity. 
This is, however, only a particular case of the general formulas dis- 
covered by Fresnel, and applying universally to intensities of reflected 
light at all incidences. The demonstration of these formulas in- 
volves some difficulties which Fresnel did not clear up, but which he, 
with marvellous sagacity, got over by suppositions somewhat of an 
empirical and hypothetical kind. To express the masses of the cor- 
responding vibrating portions of ether in the two adjacent media, we 
take lengths 7 and /) of the incident and refracted rays inversely pro- 
1 See Mr. Airy’s Tract of the Undulatory Theory. Art. 128, 
et seq. 
11* 
