1913] CONFINES OF A DIFFUSING MEDIUM 207 in which sin a = If/j,, /j, (greater than unity) "being the refractive index. In (3) 2 sin 0' cos B' dd' = d sin2 6' = ^d sin2 6, and thus (3) = yu-2 x (2) + 1 - ,jr* = - L2 - 1 + I ^ sin 20 (S2 or T2) del,.. .(4) expressing the proportion of the uniformly diffused incident light reflected in this case. Much the more important part is the light totally reflected. If //, = T5, this amounts to 5/9 or 0-5556. With the same value of //,, I find by Weddle's rule sin 26 . S*d6 == 01460, sin W . T2d0 = 0-0339. o J o Thus for light vibrating perpendicularly to the plane of incidence (4) = 0-5556 + 0-0649 = 0'6205 ; while for light vibrating in the plane of incidence (4) = 0-5556 + 0-0151 = 0'5707. The increased reflection due to the diffusion of the light is thus abundantly explained, by far the greater part being due to the total reflection which ensues when the incidence in the denser medium is somewhat oblique. '<ay take first the case where 0 > 6', that is, when the transition is from the less to the more refractive medium.