ATMOSPHERIC ACTINOMETRY. 



45 



already shown that the difference in altitude is of little importance. At all events 

 it acted in the opposite sense to tiie phenomenon which I sought to verify. As a 

 compensation, the climate of this station at Olmet is a temperate climate. The 

 place lies on the line where the culture of the vine ceases and is in every resjject 

 equal to that of Fau, in the valley of Marmanhac, and of Noalhac, in the valley of 

 Aurillac, where I had made my first observations. 



Furthermoi-e, the procedure of M. Gessard and myself was the same; we 

 exposed, from 8 o'clock a.m. till 5 o'clock p.m., vessels containing the same solution, 

 only, on account of the high temperature of Setif during the summer and of the evap- 

 oration caused by it, we had to pour into the vessels 20 cubic centimetres of oxalic 

 acid, instead of 10, and [»lace them, not upon wooden or stone supports, but upon 

 the water of a great crystallizing pan. I need not say that at Ohuet I followed 

 the same practice. It is well known that the degree of solar combustion depends 

 on the depth of the liquid, and this is the reason why the ^Ji'esent series of experi- 

 ments is not directly comparable with the preceding seiies. But it is sufficient for 

 us that the experiments made in France and in Algeria should be compai'able 

 between themselves. 



This being granted, I subjoin the results obtained by M. Gessard : 



In the following experiments, made in August and September, M. Gessai'd 

 ascertained the direction of the wind and the temperatui'e, as read on a tliennometer 



' One of the vessels was found to be submerged on this day, so that the result could not be 

 correctly ascertained. The weather on this day did not essentially differ from that of the preced- 

 ing and of the following days. 



