MR. POWER ON THE ABSORPTION OF THE SOLAR RAYS, ETC. 
41 
Fresnel’s expression for a ray polarized perpendicularly to the plane of incidence, 
that is, according - to Fresnel’s views, whose vibrations are performed in the plane of 
incidence, a result which, at first sig-ht, seems to militate ag-ainst the expression I 
have obtained for the case under consideration, viz. 
sin 2 (0— 8 ,) 
sin 2 (0 + 0j 
But I beg- to observe, 
that the juxtaposition of two heterogeneous gases of different densities under a con- 
stant pressure is not at all analogous to the case of light as conceived in the present 
communication. For, instead of heterogeneous fluids under a constant pressure, we 
have to conceive pure ether of one density in contact with pure ether of a different 
density, and therefore under a different pressure, such difference of density and press- 
ure being due to the attractions or repulsions of the grosser particles of the medium 
for the particles of the ether. We have therefore no right to make the substitution 
ii= sin 2 ^, the truth of which rests entirely on a property peculiar to gases. 
It is much more natural to suppose that the density of the ether in the interior of 
crystals does not differ much from that of the surrounding ether, so that the ratio ^ 
does not sensibly differ from unity. Replacing this ratio by unity, Mr. Green’s ex- 
pression becomes 
_cot0 / 
cot 0 tan 0 ; — tan 0 sin (0 — 0 ( ) 
cot^ ( tan 0,+ tan 0 sin ( 0 - 1 - 0 ,) 5 
1+ cot0 
the square of which gives for the intensity of the reflected ray, agreeably to 
the present theory. This curious interchange of the expressions + ^ and tari 2 (g + ay 
according to the different circumstances of the case, is very remarkable, and tends to 
throw light on the discrepancies of different theorists, as regards the direction of 
vibration. 
It is further remarkable that a similar interchange, according as we substitute 
-^-20, or 1 for the ratio occurs in the expression for the change of phase, as inves- 
tigated by Mr. Green, in the case of total reflexion at an angle greater than the 
critical angle. In fact, if 2e denote the acceleration of phase in the reflected ray, the 
following general formula will be found to result from Mr. Green’s equations, 
which transforms itself into 
tan e=~- \Zfdii 2 Q—u? sec 2 6, 
5 / 
tan e= 
1 
f/. cos 0 
MDCCCLIV. 
G 
