368 DR. MEYER WILDERMAN ON THE CHEMICAL STATICS AND DYNAMICS OF 
colourless gelatine screen, 0*12 millim. thick), in N13 = 64*5 millims. All the 
above curves were taken at a distance of the arc from quartz vessel = 118 centims. 
At the conclusion (after the photographic paper sheet was taken off') I measured also 
the deflection obtained on the drum with the total light of the arc at a distance of 
the arc from quartz vessel =89 centims. and found it to be 120 millims. (we denote 
this measurement as Nl4). The deduction period was allowed to become complete or 
almost complete in most of the curves (N8, 1.0, 11, 12). We get for the law of 
intensity : 
H8 2 x 76 + 69 + 71 ■- = 100*5 x 10 4 , 118 2 x 69 + 7 — = 97*7 x 10 4 and 89 2 x 120 = 95*0 x 10 4 . 
9 
Calculating the thermo E.M.F. created by light, we get: the rise of temperature 
i t j. (0°*03 to 0°*045)x27 2 x 19*8x9*2 _ n0 . niQ n o. nno n dir 
of the exposed plate = '- U 8> x m x 17 ~ 0 5-° 013 t0 ° °° 9 dr 
= 0*00079 volt, the sensitiveness of Nalder Nl = 93*9 centims. per 10“ 6 ampere, 
shunt of galvanometer = 40 ohms, the resistance of the solution in quartz vessel 
= 43 ohms, &c., therefore the thermo E.M.F. = 0*74 to 1*1 per cent, of the total 
deflection of the total light (without screen). 
Thus we get :— 
Total light. 
Red gelatine 
screen. 
Blue screen. 
Yellow-green 
screen. 
Total E.M.F., in millims . 
70'2 (corr. 72*2) 
5 
23 
5 
The thermo E.M.F., in \ 
O'54 to 0'8 
0'39 to 0-57 
0-3 to 0'45 
0'25 to 0'4 
millims./ 
E.M.F. at a constant tern-1 
69'4 to 69'8 
4'4 to 4'6 
22-5 to 22-7 
4'6 to 4'75 
perature, in millims . J 
In per cent, of the total 1 
light.J 
100 
6'3 to 6'6 
32'4 to 32'7 
6'ti to 6'8 
Here we find for the arc : (l) that the light passing the red screen gives a smaller 
deflection than the light passing the blue gelatine screen, while between the red and 
yellow-green screens no essential difference is found ; (2) that all parts of the spectrum 
give E.M.F.’s at a constant temperature ( i.e ., also the red and yellow-green parts of 
the spectrum). Contrary to this, we found with acetylene that the red screen gave 
greater deflections than the yellow-green, i.e., that two maxima are existing, one in 
the red, the other in the blue. It follows from this that the arc is richer in blue, the 
acetylene in red rays. 
I next proceed to the account of comparative experiments, where either the con¬ 
centrations of the same solutions or the temperature were changed. All these 
experiments had to be carried out in as short a time as possible, to avoid the effect 
of time after previous illumination. On the other hand, really good experiments 
require very small values of the E.M.F. in the dark, which is not possible without 
