ATMOSPHERIC ACTINOMETRY 



Tlie must active combustions correspoiui to tlie highest nia.xiiiiiiiii teinpenitures, 

 but only because both of them indicate, each in its own way, the presence of a 

 livelier ami uioie active sunli^lit. AVlicii the sky is overcast or shows cuimili, 

 the solar combustion may be more powerful than avIhmi there are cirri, even though 

 tlie ma.ximum temperature should be lower. 



In no c.ise, as will be seen, has the temperature of the solution I'isen to a suffi- 

 ciently liigh level to affect the chemical combustion which takes place there. A\'e 

 may, however, if we wish it, secure ourselves against this cause of ei-ror by causing 

 the light vessels which contain the solution of oxalic acid, to fl0.1t on a water-b.ith. 

 They will tlien, during the day on wliicli they are exposed to tin- sun, be heated a 

 few degrees only. Thi.s is a method wliicli I have a(l(.i)ted only iluiing the hottest 

 and driest day.s. The water-b.ith served as much to lestraiu eva[ioration as to 

 prevent heating of the solution. 



INFLUENCE OF THE AGE OF THE SOLUTION. 



We now reach an uiiexjiei-ted fart, namely : that a fresh solution of o.x.alic 

 acid does not behave like an oldei' solution of the same .strength, and appears much 

 Mioi-e refractoiy to the action of the sun. It becomes sensitive only very slowly, 

 and it requires even several weeks for that end, when it is kcjit in diffused light. 

 -^■P- — On September 5, 1885, I coniparr.l an dd .solution of ox.alic acid, con- 

 taining ^^ equivalent (1.575 grm.) of this acid per litre, with another 

 liquid, which I j)repared at th.tt moment, of the same strength. The com- 

 mon titre of these two solutions aiiiouiifcd to 22.8 c. c. of lime-w.ater 

 for 20 cubic centimetres. 



At the close of the day (8ei)tend)er r)th), which had been ijithor 

 ^"aSy> ^-^^o insolated vessels containing the older liquid titrated together 



