884 PEOFESSOE BTJNSEN AIV T) DE. H. E. EOSCOE’S PHOTO-CHEMICAIL EESEAECHES. 
Tho numbers contained in column VIII. of Table I. must therefore be multiplied by 
this constant, 2-005, in order to obtain the action (wj wMch the flame would hare pro- 
duced if no loss of light from mica-plates, water-screen, or by reflexion from the inso- 
lation-vessel had occurred. The following numbers give the values of the noi-mal 
action effected when the gas issued at the corresponding rates g 
9- 
w,. 
5-950 
27-86 
4-673 
18-90 
3-839 
13-60 
3-053 
8-30 
If the values of A, B, and C are calculated from the above values of g and lo, in the 
following series of powers of (5--^), 
w,=A+B(5»^)+C(5-^)^-l- ■ ■ . . , 
it is seen that the value of C is so small, that the third term C{b--gf may be struck out. 
The values of A and B, calculated according to the method of least squares, give the 
folio-wing simple equation, 
^ w,=21-34{l-0-3153(5™^)} (2.) 
From this it is seen that, although tlm rates at which the gas issues differ considerably, 
the increase in the action effected by the flame is, within the obser\ed limits, directly 
proportional to the increase in the rate of issue of the gas. The straight line (flg. 2, 
Plate XLIV.) shows how closely the observations agree with this assumption. The 
abscissse represent the volumes (in cub. cent.) of carbonic oxide, measured at 0° and 0“-76, 
which escaped from the burner in one second ; and the ordinates give the correspond- 
ing chemical actions observed in divisions of the instrument in one minute, when the 
distance from the burner to the insolation-vessel was 176 millims. The observations 
are denoted in the figure by black dots on or near the line. 
By means of the foregoing equation (2.) it is easy to calculate, from the chemical 
action observed for any particular rate of issue of the gas lying between 3 and 6 cub. 
cent, per second, what the chemical action would have been if the gas had issued at the 
rate ^=5 instead of at the observed rate, other circumstances remaining of coui'se the 
same. 
The standard flame which we employ to compare all the soui'ces of light we have to 
measure may be thus defined :■ — “ The standard flame is that produced by the free com- 
bustion in atmospheric air of carbonic oxide gas issuing at the rate of 5 cub. cent, per 
second {reduced to 0° and 0“-76) /rom a circular platinum burner 7 millims. in diameter, 
under a pressure differing but very slightly from that of the atmosphere.'' 
By means of the standard flame we are enabled to reduce the indications of different 
instruments to the same unit of luminous intensity, and thus to render them comparable. 
For this purpose we define the photometric unit for the chemically active rays to be 
that amount of action which is produced in one minute by a standard flame placed at a 
