88 Mr. Claudet on different Properiies of Solar Radiation 



The interesting calculations of M. Petit*, Director of the 

 Observatory of Toulouse, not only render probable the exist- 

 ence of small satellites, but tend to establish the identity of a 

 body revolving round the earth in about 3 hours 20 minutes. 



I have endeavoured in this paper to point out the import- 

 ance of marking the exact time and place of disappearance; 

 for although if the place is found at any point of the path by two 

 different observers, theoretically the parallax could be ascer- 

 tained, in practice this method is beset with great difficulties. 



It seems to me that the splitting of the falling stars, like a 

 rocket and the trains of light, a phaenomenon often witnessed, 

 might, if other circumstances were favourable to the explana- 

 tion, be accounted for by supposing the star to graze the sur- 

 face of the shadow before absolute immersion. 



Close to the earth's surface, the linear distance traversed in 

 the penumbra must be small; but at greater distances this 

 will increase, and perhaps render the disappearance less sud- 

 den. If the distance comes out large, it will of course be ne- 

 cessary to recalculate it, supposing the surface of the shadow 

 to be conical and not cylindrical. 



23 St. James's Place, Jan. 10, 1848. 



XIV. On different Properties of Solar Radiation producing 

 or preventing a deposit of Mercury on Silver Plates coated, 

 •with Iodine, or its compounds with Bromine or Chlorine, 

 modifed by Coloured Glass Media and the Vapours of the 

 Atmosphere. By A. Clavd^t, Esq. Communicated by 8ir 

 David Bkewster, F.R.S. Sr^.f 



FROM the commencement of photography it has been 

 known that the red, orange, and yellow rays exert but a 

 very feeble photogenic influence on the Daguerreotype plate. 

 The experiments of several philosophers, especially those of 

 Sir J. Herschel on photogenic papers, published in February 

 1840, prove that this action is more particularly confined to 

 the most refrangible part of the prismatic spectrum, commen- 

 cing from the space found covered by the blue rays and ex- 

 tending to the extremity of the violet, and sometimes even 

 beyond it. 



In 1839, Sir J. Herschel observed that the red" rays exer- 

 cised on several photogenic papers an antagonistic action to 

 the photogenic rays, modifying their effect. Contrary to this, 

 in ISil, M. Ed. Becquerel presented to the Paris Academy 

 of Sciences a memoir, in which he announced that the red, 



* See the Comptes Rendus, October 12, 1846, and August 9, 1847. 

 t From the Philosophical Transactions for 1847, part ii.; having been 

 received by the Royal Society June 10, and read June 17, 1847. 



