42 ATMOSPHERIC ACTINOMETRY 



different chapters of this JMemuir have shown, may therefore differ in the (|ualit\ 

 of the effects which it produces. AH these facts lend to the study of chemical 

 radiation, an importance of the highest rank, and I shall consider myself veiy 

 happy, if the fti'st results contained in this paper shall lead men of science to 

 new researches. 



SUMMARY. 



1. The oxidation of oxalic acid in a weak solution takes place mainly, and 

 almost exclusiv^ely, under the influence of the <heniical rays of solar light ; it can, 

 therefore, be used as an actinometric measure. 



2. It depends on the concentration of the liquid, which for the best lesults 

 should not exceed about three grammes per litre. 



3. With an equal volume of solution, combustion deci'eases as depth increases ; 

 there is an absorption of chemical rays, although the Ii(|uid is and remains verv 

 transparent. 



4. For equal depths of li(|uid, cnijilnistion is propc>iii<iiial to the surface, and 

 consequently also to the volume. 



5. It depends on the age of the solution, that is to say, of tlie time which 

 has elapsed since preparation. As it grows oldei-, an uxalic suliitidii lieconies ninre 

 sensitive, and attains a certain niaxiniuin wliicli is (|iiiic stal'K- and (|iiite regular. 

 It is well to wait till this state of sensitiveness has been produced. 



6. The daily combustion, such as is measured with sterilized liquids, varies 

 from one day to another much more than any other meteorological phenomenon, 

 and while subject to the influence of what we call " fine weather " and " o\-ercast 

 w^eather," it manifests very clearly other influences which are less \nsible. 



7. It shows also the influence of the seasons, and manifestly exhibits a maxi- 

 mum in spring. 



8. It is but feebly subject to the influence of altitude. 



9. On the other hand, it betrays so strongly the presence of divers oxidizable 

 essences or substances in the aii-, that we must consider local and daily variations 

 as due to the presence in the atmosphere of actinic clouds, which are discoverable 

 only by the redtiction and aV)sorption -w hich they produce in the chemical radiations 

 of sunlight. 



H>. The atmosphere of extreme nortlieni regions is less absorbent than that 

 of oiii' temperate zones, and, consequently, at the same hours of the day, actinic 

 radiation is more powerful, at the level of the soil, in the north than at the centre 

 of Europe. 



