]80 Mrs Somerville on the 



Height of Bareges, a Hamlet of the " Commune of Betpouey? 



Extract of a Letter from Mrs Somervllle. to M. Arago, detailing 

 some Experiments concerning the Transmission ()f the Che- 

 mical Rays of the Solar Spectrum through different Media. 



IN the account of the meeting of L 1 Academic des Sciences on 

 the 21st of December J835 (Compte Rendu, p. 508), it is 

 stated that M. Arago, after having repeated what was most es- 

 sential in those experiments by which M. Melloni proves that 

 the solar rays, while preserving all their luminous properties, 

 may be deprived of their calorific power, remarked, that 

 there was another point of view in which the subject might be 

 investigated. He said it would be important to inquire if the 

 means employed by M. Melloni, or other analogous ones, would 

 not enable us to deprive the solar rays of their chemical proper- 

 ties also ; or, in other words, if, of the three properties which light 

 possesses when it reaches us from the sun, 1st, That of illumi- 

 nating ; 2d, That of heating ; and> 3d, That of destroying or 

 exciting chemical combination, we could not separate the latter 

 two, and retain its simple illuminating power. This experiment, 

 remarked M. Arago, would probably lead to curious results, 

 and I last week almost yielded to the temptation of undertaking 

 the investigation. But, as possibly M. Melloni may have him- 

 self thought of it, though quite silent about it in his memoir, I 

 think I had better not prosecute the subjects till after consulting 

 the learned Italian philosopher. 



The motives which I had in 1835, said M. Arago, at the 

 meeting of the Academy on the 17th of October 1836, not to 

 interfere in researches which so directly conducted M. Melloni 

 to these beautiful discoveries, still subsist. I shall, therefore, ab- 

 stain from stating some results to which I have arrived concern- 

 ing the absorption or interception of the chemical rays. Every 



