34 ATMOSPHERIC ACTINOMETRY 



respoiiiliug figures are '_'(i [>er cent and 11 percent; tliis >liu\vs that not only does 

 the sensitiveness of the oxalic solution increase in consequence of insolation, but the 

 gain continues during the night. Souic cxjterinients of the same kind, which I will 

 not now explain in detail, prove that this excitation of sensitiveness b}' means of inso- 

 lation, endures even to the second day after, in a solution which is kept in the dark 

 alter having been exposed for a day to the sun. It is only after three days, there- 

 fore, that traces of sensitiveness are no longer discernible. By that time, the 

 insolated solution has nearly' returned to the degree of sen-sitiveness which the 

 mother liipiid possessed, which seems thus to coirespoiid to a kind of equilibrium. 

 It is in fact remarkable that the different sen.sitive li(piids which I have used in niv 

 long experiments and which were prepared at very different times, with the single 

 precaution that they were not to be used before the lapse of several months, had all 

 of them, at the moment when I used them, very neaily the same sensitiveness. It 

 was on September 8th and 9th that I had to change ni}^ solutions at Mont Dore, 

 and I availed myself of the fact that these two days were but indifferently fair, to 

 interru[it my series and to compare again and again the old liquid with the new. 

 The title was always the same for both. Mi'. Elfving compared likewise two solu- 

 tions which I had sent him a year apart, and found in four days of experimenting 

 the following corresponding figures for the old and the new: 



The old solution was a little more sensitive, which is the usual rule. But 

 the difference was trifling, and thus our former statement was confirmed (page D). 

 The oxalic solution, kept in diffused light, reaches a fairly constant sensitiveness in 

 a few weeks, but this maximum, altlidugli stable, is not a maxmiiim. maximorvm. 

 It may be temi»orarily exalted in the sun, continue if the illumination continues, 

 and return to its original leve-l .aftei' some days of darkness. 



in order to make this conclusion it'all\ v;duable, we have to overcome one last 

 olijection. Might it not ha[)pen that the increase of combustion discovei'ed on the 

 .second day in a vessel which li.'nl been insolated on the day before, might mean 

 simply the suppression of the "dead time" at the beginning? Starting earlier, the 

 combustion might better utilize the good hours of the day, and thus be enabled to 

 go farther. A priori, the intervention of this cause does not seem to explain suffi- 

 ciently the great difference observed. But it is safer to consult experience. It will be 



