38 ATMOSPHERIC ACTINOMETRY 



I liiivc left aiside, in all which ]nvfi'(les, tlie tjuestioii of the laerhauisra cou- 

 uected with l)oth seusitizatioii and condjiistion. The former goes on when the 

 solution is sheltered from the aii', and lan take ]>]aee only ^>y a new arrantrement 

 of inojfcult's. Coiid)ustioii, on the othei- hand, takes jdace in contact witli tin- air 

 ami |H>ssil)l\ with the foi'unition of ozone or of hydroj^en peroxide. iliat is a t[ue8- 

 tion which must be iuvestigatetl l>y itself. I purpose here only to put in «'\ iilence, 

 as regards the constitution of the atmosphere, some properties and a \arialiilit\ of 

 effects, Hot hitherto oljserved. 



^) 



IMK'IT.ItKOT.OfilcAL, IlYtilKXIC, AXD AgPJCULTUUAL EiTECTS. 



if we m>w leturn, with the residts which we have obtained, to our investiga- 

 tion of the causes w liirh provoke the rapitl dc\ clupment of vegetation iu the extreme 

 northern regions, we see that those regions are superior to ours in a twofold 

 aspect. 



1. Tiiat cause which de])eiids on the constitution of their atmosphere consists in 

 this, that the ab.sdrption of the chemical radiations of solar light is there less great 

 than w ith us. The actinic power at the level of the soil exceeds that which we 

 have observed around ourselves at different hours of the day, and that in spite of 

 a lower sun and a greater thickness of atmosphere, ^vhicll the rays must traverse. 

 These differences are due mainly to the fact that vegetation in the noi'th sends 

 into the air fewer oxidizable substances to form a screen. 



'2. The other |)oint of superiority connected with the geographical situation 

 consists in tlii>. that in the extreme north, dui-ing the |icriod of vegetation, the 

 days are longer than in our temjjerate zones, and that tiic actinic power, at least 

 so far as it may Ije measured by a solution of oxalic acid, increases more rajiidly 

 than the length of the day, and tliis out of all proportion. After a ]>('i'ioil of pre])a- 

 ration, combustion begins, then accelerates so rapidly as to make up for time lost 

 at the beginning, and linally, towards evening, reaches uiuisnally high figures, such 

 as arc unknown to our regions. It is in this way that coinbustion has risen to 



37 and fS!) per cent on Sej)tcmbci- 2 and \. Iss7, 

 7'.» and SO ]»er cent on Sei>tend)er '.» and 1 1, 1 SSS, 

 7r> pel' cent on ,\ul;. -7. Isss .-it Helsingfoi-s. 



and this at a time w lien the highest ligures. relatix ely to the same j)eriods and with 

 the same solutions, did not exceed oO per cent and were even sometimes much 

 lower in our country. In order to reach figures e«|ual to those olttained in the Gulf 

 of Finland, it was necessary for nic in France to accumulate iiinni iii\ vessels the 



