20 ATMOSPHERIC A(TINO>rF.TRY 



this action as far as possible fi-om that of llie roughness of the walls, a 

 fourth vessel is brought up to the same degree of opacity as No. 3, by 

 rubbing it externally with chalk diffused in water. Finally, to increase 

 the (piautity of fatty matter present in the liquid, and also, in order to 

 see the effect which a little opacity of the liijuid may there produce, new 

 vessels, Nos. 1', 2', and 3', have lieen prepared like the vessels Nos. 1, 2, 

 and 3, simply addiug to each two drops, in other words 5 milligrammes, 

 of fatty matter. 



These were the residts: 



Combustion. 



Vessel No. i, clean sides 33 ^ 



" ** ^ ** << ^ 



2. 33 ^ 



" " 3, dull sides, greasy surface 29 ^ 



" " 4, " " (chalk) 32^ 



" " i', like I, plus 2 drops of milk 16 j^ 



2 . 2. 17 i 



3 . 3. 17 ^ 



Other experiments, made the following )'ears, and the detailed reports of 

 which have been lost, confirm these first results, and show that the fatty matter 

 contained in a liquid or spread as an invisible layer over the surface, like that 

 which covers the walls of a bell jar placed over the ves.sel containing oxalic acid, 

 diminishes the actinic effect of the .solar rays. 



Finally, it is the same w ith many substances, more or less easily oxidizable, 

 which also exert a protecting, or at least a retarding, effect upon tiie influence of 

 the chemical radiations. Siudi is, for instance, alcohol. 



Msp. — On the 2nth June, 1885, two vessels with 10 c. c. of an o.valic acid solu- 

 tion, containing ^'5^ equivalent per litre, gave me a combustion of 37 per 

 cent, the same for both. Two other vessels, exactly alike, which have 

 received an addition of 2.;") c. c. alcohol of 90 per cent, gave me onlv a 

 combustion of 21 per cent. 

 Mcp. — On September 14, 1888, two vessels with a solution of ^^ equivalent of 

 oxalic acid, gave me identical combustions, rising as high as 10 per cent. 

 They amounted only to 4 per cent in two like vessels, to which a few diops 

 of oil of oranges had been added, so that the essential oil and the alcohol 

 have acted similarly. 

 I have made numerous experiments with divers substances which were oxidi- 

 zing or oxidizable, the <letails of which have been lost. In a general way I have 

 found that the former increase the combustion of oxalic acid, while the others 

 retard it. 



