PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 607 
On passing the 
On passing the 
On passing the 
On passing the 
tirst surface 
second surface . 
thh’d surface . 
fourth surface . 
(1-f) 
The total amount of transmitted light is in this case, therefore, (1 — fi)^; and as § 
is greater than the amount of transmitted light is larger than in the case when air 
was contained between the plates. 
If the media are placed in the following order, air, water, glass, air, glass, air ; and 
If the coefficient of reflexion between air and water 
If the coefficient of reflexion between water and glass 
If the coefficient of reflexion between glass and air =g>, 
a repetition of the foregoing reasoning shows that the transmitted light is not 
but 
It is easy from these considerations to determine the amount of light transmitted by 
two diactinous glass plates enclosing a column of water. Let § represent the coefficient 
of reflexion between ah’ and glass, ^ j between water and glass, h the length of the 
enclosed column of water, and ^ the length of a column of water by passing through 
which nine-tenths of the light is extinguished ; we then have the unit amount of light 
reduced. 
After passing the sm’face r (fig. 2) (1 ~ g>) 
After passing the sm’face (fig. 2) (l"~g')(l~?i) 
After traversing the space fi’om to (I— f)(I— 
After passing the surface from (I— f)(l— 
After passing the surface from (1 — ^)^(1— 
If lo represent the amount of incident light, and I that of the transmitted light, ^ of 
the rmit amount of incident light is transmitted. Hence we have 
( 7 .) 
and 
log[^(l-§)2(I-gi)^] 
( 8 .) 
The value of ^ for our cylinders filled with air is, as has been shown, 0’0509, and 
the value of calculated from the index of refraction from crown glass to water, 
i=IT718, by means of the formula , is found to be 0’006257. An experi- 
ment with columns of water of h millimetre thickness gave the following values for I# 
(the light measured without interposed cylinder) and I (with interposed cylinder). The 
values of a contained in the lowest horizontal line are calculated according to formula (8.). 
4 K 2 
