342 DR. MEYER WILDERMAN ON THE CHEMICAL STATICS AND DYNAMICS OF 
its rise of temperature, greater; the other is an E.M.F. due to light at a constant 
temperature, the chemical potential of the exposed plate becoming greater under the 
action of light. 
Similar results are obtained with the constant arc, and the still more constant 
acetylene light, for systems (Ag-BrAg, NaBr solution, Ag-BrAg), (Ag-ClAg, NaCl 
solution, Ag-ClAg), (Ag-IAg, KI solution, Agl-Ag), &c. 
In the experiments carried out with the system Ag-BrAg plates in a 0‘1 normal 
NaBr solution, e.g., on July 29, 1903 (a), acetylene light was used at a distance of 
116 centims. from the quartz vessel. We get: total E.M.F. observed = 8T6 millims. 
or 7 7 x 10 h volt; the thermo E.M.F. = 0’8 x 10~ 6 to 1*2 x 10 -b volt; the thermo 
E.M.F. = DO per cent, to 15 per cent, of the total E.M.F. 
§ 3. The Rays of all Wave-lengths act both “ Chemically ” and as “ Heat Rays,” 
only in different Degrees. 
The next question was : Is the E.M.F. produced by the red part of the spectrum 
solely due to its heating action, or does it act “ chemically ” in the same manner as 
blue, violet, &c., rays—the so-called “actinic rays” of light? For this the same 
combinations (Ag, AgN0 3 solution, Ag, Ag-BrAg, NaBr solution, Ag-BrAg, &c.) 
were exposed to light passing different coloured screens, and the total E.M.F. so 
obtained compared with the thermo E.M.F. corresponding to the heating effect of the 
coloured light. For the first system the arc, and for the second, as before, the arc and 
the acetylene lights were used. 
The relative values of the thermo E.M.F.’s of the total light and of the total light, 
passing the different screens was first determined from the heating effect of the same. 
A specially made thermopile with 40 iron-nickel junctions (made dead black) was 
introduced into the air space of the quartz vessel, placed in the bath 8 centims. behind 
the quartz window (as in all our subsequent experiments with the different galvanic 
cells) and connected with the dead-beat galvanometer (Nalder Nl), used for 
photographing all the curves in this investigation. 
The deflections of the galvanometer for the total light without screens and the 
total light passing a series of screens (without dye, red, green, yellow and blue) 
prepared for me from thin gelatine by Mr. Hilger, and placed before the quartz 
window of the bath, were photographed. The thickness of each screen was also 
measured so as to be able to introduce the correction for the absorption by gelatine ; 
the photographed deflections so obtained gave the following results :—• 
With the same source of light (arc, v = 6'6, A = 60, distance from quartz 
vessel = 36 centims.) we got: total light, without screen, gave 89’5 centims. deflection ; 
the same light passing the gelatine screen (0125 millim. thick), 62'9 centims. ; the 
red gelatine screen (0'08 millim. thick), 65'5 centims. ; the yellow-green gelatine 
screen (0H1 millim. thick), 41‘0 centims. ; the blue gelatine screen (OHO millim. 
thick), 49’0 centims. deflection. 
