AND THE ACTINIC CONSTITUTION OF THE ATMOSPHERE. 11 



Iialf-deci-normal solution exposed to tlie sun. Fiiitlu rmore tlie state of the sky has 

 been recorded and the pi'incipal incidents of the dny of insolation. 



Special attention has been paid to vei'ifying the solar and antisolar lights' 

 which were very frequent during the first yeai's in which these observations were 

 made and which have never been absent since that time. I have desci'ibed the 

 aspect they assumed in the countries in which I began my observations. The more 

 1 study them, the more I consider them as solely due to the presence of aqueous 

 vapor at very great heights in the atmosphere. We shall have to examine, from 

 this point of view, their influence on the phenomena of solar combustion. 



The tables which follow ai'e also intended to show the very considerable 

 variation which the quantities of oxalic acid consumed present from day to day. 

 The combustion, which is almost completely absent on cloudy oi' rainy days, may 

 reach or even exceed 50 per cent of the acid during bright and luminous days. But 

 there are also some very bright days, during which combustion is feeble, and twice 

 it has happened that I was unable to take photographs for want of proper light, 

 being deceived by the apparent brightness of the day on which I was working. 



I shall quote ray observations very nearly in the oixler in which I made them, 

 from the moment when I had I'egulated the process of measurement ; and in con- 

 nection with each one of these sets of observations I shall cite the facts which 

 they have revealed to me and which subsequent observations have only confirmed. 



OBSERVATIONS OF THE YEAR 18S5. 



Made at Fau (Cautal). Altitude 800 metres. Country of meadows and of 

 woods. Volcanic soil. (Andesite and basalt of the plateau.) 



I have inserted above (page 8) some observations which I made at the end of 

 August with the solution in a conical glass. The combustion is a little less rapid 

 than in the vessels of Bohemian glass which I used in experiments of a later date. 

 Here follow those made in September and October. S. and A. S. i-epresent solar 

 lights in the west and anti-solar lights. 



' See, on this subject, a note inserted in the CampUs Eauhis ik I'Acad/mie <ks Sciences, \o\. 

 xcix, 1). 714. 



