882 PEOFESSOE BUjS-SEN AjSD DE. H. E. EOSCOE’S PHOTO-CKDnCAL EESEAECHES. 
The observed action [w) does not, however, express the total action of the carbonic 
oxide flame, for between the burner and the sensitive gas several screens were placed. 
The light had to pass, in the first place, through the water-screen, then through two 
plates of mica, and also through the glass sides of the insolation-vessel before it reached 
the mixture of chlorine and hydrogen. Hence in order to find what the action would 
have been if the light had not been diminished by passing thi’ough these screens, we 
must multiply these values of w by a constant dependent on the absorbent character 
of these media. This constant, which we will call K, is made up of three parts : — 
1. The diminution which the light sufiers in passing through the mica-plates =L. 
2. The diminution the light suffers by passing through the water-screen 
3. The light lost by reflexion from the surfaces of the insolation-vessel =X. 
The value of L is easily found from the coefficient of reflexion for mica, which we 
have already determined'*. From the experimental number o=0T011, the value of 
L”1‘450 is found from the equation L= 
I + 3g 
l-g- 
We determined the value of M by 
observing, twelve times successively, the action effected in 30 seconds by a constant gas 
flame, the water-screen being alternately placed before the flame and removed. The 
following Table contains the results of these observations : — 
Table II. 
Xo. 
Action without screen. 
Action with screen. 
1 
12-69 
9-25 
2 
12-85 
9-59 
3 
12-46 
9-81 
4 
12-31 
9-59 
5 
13-47 
9-00 
Mean ... 
12-76 
9-45 
By dividing the numbers in the second column by the corresponding numbers in the 
third, the mean value of M=1'351 is obtained. 
The value of N is arrived at by help of the following considerations : — Let A Ao 
(fig. 1, Plate XLIII.) represent the surface of the insolation- vessel nearest the flame, and 
B Bi that furthest from the flame. The space between these two surfaces being sup- 
posed to be filled with sensitive gas, let 1 represent the intensity of the light falling 
perpendicularly on the insolation- vessel ; and let r= 
1 + g 
represent the amount of light 
reflected from both surfaces of the side A of the insolation-vessel, when § is the 
coefficient of reflexion for glass and air; and let represent the amoimt of 
light remaining after passing from A to B=7?, when a represents the coefficient o± 
-Q 
extinction of the chlorine and hydrogen gas; and lastly, let (7=1 — represent the 
* Philosophical Transactions, 1857, p. 609. 
