80 Intelligence and Miscellaneous Articles, 



but it would not be justifiable to attribute to this vapour itself the 

 presence of telluric bands." 



Hence it follows from all this, that aqueous vapour in that parti- 

 cular physical condition in which it constitutes clouds and atmo- 

 spheric vapours, cannot be invoked as the cause of the telluric rays 

 of the solar spectrum ; and hence the conclusion which Secchi draws 

 regarding the constitution of the planetary atmosphere cannot be con- 

 sidered to be well founded. 



Later, in a communication on the spectrum of Jupiter, Secchi 

 maintains his primary conclusion and says, " On this occasion I have 

 confirmed anew the influence of fogs on the terrestrial atmospheric 

 rays." 



I have continued a long series of observations under the most diverse 

 atmospherical circumstances, but taking care only to use the direct 

 light of the sun, so as not to complicate the .question by these cir- 

 cumstances of foreign reflexions, difficult to estimate, and which 

 have thrown such a regrettable confusion into the observations 

 of Father Secchi. 



The whole of these observations have shown me that the vapour 

 of water in the state of cloud or of atmospheric vapour did not 

 appear to act*, but that it is aqueous vapour in the state of elastic 

 fluid which has an important part in the production of the telluric 

 rays of the solar spectrum. 



For instance, on the 5th of July 1864, the weather being clear, 

 pure, and hot, a telluric group measured on our scale had the inten- 

 sity 15, the sun being 4 o- 30 above the horizon ; while on the 27th of 

 December, 1864, for the same height of the sun, the weather equally 

 clear but so dry that the dew-point was 8° below zero, the same 

 group had no more than the intensity 4 on the same scale. 



An experiment to verify this important point has recently been 

 made at the central government establishment for the construction 

 of lighthouses ; it has given a confirmatory result ; I expect to make 

 it on a still more considerable scale, where the phenomenon can 

 be studied as it deserves. 



Two years ago, when publishing my first spectral studies on the 

 earth's atmosphere, I expressed the opinion that this study would 

 lead later to the knowledge of the atmospheres of planets. I have 

 at present the pleasure of seeing that this expectation is being more 

 and more realized ; for apart from the above facts, the recent results 

 obtained by Messrs. Huggins and Miller, who have seen new rays 

 in the spectra of the planets, are a confirmation of these ideas. — 

 Comptes Rendus, January 1865. 



* Solar light which had traversed a fog or a mist gave me telluric rays 

 no more iatense than when the sky was clear, with a dew-point just as high 

 (other circumstances being the same). The dew-point was determined by 

 means of Regnault's condensation hygrometer. 



