PEOFESSOE BimSEN AINB DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 883 
intensity of the original unit amount of light after having passed through the side A 
of the insolation- vessel. For the sake of clearness, we have represented the rays of 
light, which are in reality reflected perpendicularly from the surface B Bj, by the lines 
AB, BAj, AjBj, &c. At these several points the unit quantity of light falling on the 
insolation-vessel has the following intensities ; — 
At A in the line AB the intensity is d. 
At B in the line BA the intensity is dy. 
At B in the line BAj the intensity is dyr. 
At Ai in the line BAj the intensity is dy^r. 
At Ai in the line AjBj the intensity is dy^r^. 
At Bi in the line AjBj the intensity is dy^r^. 
At Bi in the line BjAg the intensity is dy^r^. 
At Aj in the line BjAg the intensity is (ZyV®. 
&c. 
Hence the chemical action proportional to these various intensities is found to be 
(Z/3 in the line AB. 
dyrj3 in the line BAj. 
The sum of these actions is, however, 
d(3( 1 -f- yr -f- y -j- y ^ 
dy^r^j3 in the line AjB,. 
dy^r^(3 in the line BjAa. 
dl3 
■)=i 
-yr 
1 
1 —yr 
or, as d=l — r, we have 
We can therefore eliminate the error arising from the inflnite number of reflexions 
which the light sufiers in the interior of the insolation-vessel, by multiplying the action, 
as read ofl* on the scale of the instrument, by the factor 
( 1 -) 
The numbers thus obtained represent the amount of photo-chemical action which would 
have been observed if the sensitive gas had not been suiTounded by a reflecting medium. 
In the third part of our researches* we determined the value of ^-0-0509 and 
a=0-00427 for the flame of coal-gas; = 0-0136 for the difi'use cloudless zenith light of 
morning; and 052=0-0174 for the cloudless zenith light of evening. The depth of the 
insolation-vessel was /i = 9-4 millims. When these values are substituted in formula (1.), 
N is found to be equal to 1-010 for a coal-gas flame; 
N is found to be equal to 1-028 for morning zenith light of an unclouded sky; 
N IS found to be equal to 1-034 for evening zenith light of an unclouded sky; 
and if we take the mean of these closely agreeing numbers, N= 1-024, as representing 
the loss by reflexion of the flame of carbonic oxide, we have, as the value of the product 
K=2-005. 
* PMosophical Transactions, 1857 , p. 605 , &c. 
