U ATMOSPHERIC ACTINOMETRY 



days ill August, meutioiied ou page 8, if we bear in luiiul that the experimeuts 

 mentioned on that page were made in a cone-shaped glass, capable of holding the 

 l>ulb of a thermometer and not, like those made in September, with shallow vessels 

 in which the figures would have been much higher. 



One might be tempted to see here the effect of the lessened length <>f days. 

 liut, in order to avoid this influence, the length of exposure has been everywhere 

 precisely the same: from 8.30 a.m. to 4.30 p.m. There is, therefore, an influence 

 due to the seasons, which we must also endeavor to trace back to its true cause. 

 Fi>r this purpose we can only collect the greatest possilde amount of evidence. 



RESULTS OF OIJSEKVATIOXS SIADE IN 188G AND 1887. 



I made for this end several series of experiments in 1886 and 1887, at Paris, 

 in the Cantal, and at Orcines, at the foot of the Puy-de-Dome. Unfortunately I 

 cannot report them here in detail, having mislaid the papeis which contained the 

 record. I can only indicate the general results which I iiave ivtained in my 

 memory, because they served as a starting-point for new investigations. In the 

 first place I again found evidence of the almost perfect independence between the 

 degree of solar combustion of oxalic acid, and the occurrence of .solar and anti-solar 

 lights. If there are any exami)les of coincidence between an active combustion 

 and the presence of such lights, it is because these lights appear only in fine 

 w^eather. But there are also other cases in whicL combustion is very rajiid and 

 when those lights are altogether missing. If they play any part at all, it seems to 

 be one quite secondary, and this view agrees very fairly with the hypothesis that 

 the phenomenon is due to the presence of aqueous vapors in the uppci- regions of 

 the atmosphere. It i.s, of course, well known that litpiid water or water in the 

 form of steam influences the activity of actinic combustion very little. 



Another very inq)ortant result is this: that the maxima of the figures of com- 

 bustion during the finest days are higher in spring than in summer. The difference 

 did not strike me as quite so marked as between summer and autumn. As to the 

 maxiiiiuiu in spring I have always found it very clearly marked during observa- 

 tions carried on for four years, and an example of this will be found, unfortunately 

 too limited in its nature, when I shall speak of my expeiiments of 1888. 



The maximum in spring appears alike in Paris and in the country. But I 

 have also found that solar combustion was less intense in Paris than in the Cantal 

 or in the Puy-de-Dome; this difference appears not only in the high figures 

 connected with the oxalic acid, but I have ft)und it also in a long series of 

 experiments, which I h.-xd undertaken in order to study the transformations which 



