158 ANNUAL OF SCIENTIFIC DISCOVERY. 



To these facts, or to their interpretation, M. Thenard would oppose the 

 following experiment which he has communicated to the Philomathic Society. 

 l<t Huilim tlie niirht he disinsolated a sheet of common paper, by exposing 

 it to the \a~por of water for an hour. 2d. He then divided the paper into tAvo 

 jurts; one was laid aside for comparison, the other was rolled up and placed 

 in a irlass tube, to one end of which ozonized oxygen was supplied; at the 

 end of a quarter of an hour the ozone was distinctly perceived at the other 

 extremity; the paper was then withdrawn. 3d. This paper, used in the same 

 manner as M. Niepce's insolated paper, produced the same effects; the paper 

 kept for comparison produced none of them. 4th. A paper treated with 

 chlorine or nitrate of silver, and then ozonized, gave, on the contrary, no 

 sensible result. 5th. Common paper, ozonized and kept for some time in a 

 test tube, disengages a smell which is not that of ozone, but that of a very 

 diffusible essence. What shall we conclude from this? added M. Thenard, 

 That the phenomena of insolation described by M. Niepce are chemical 

 phenomena, determined indirectly by the light, Avhich acts in this matter 

 only as an intermediate agent. 



The subject has also been investigated by M. Laborde, who is led by his 

 experiments to conclude that the active agent "is an emanation, not a radia- 

 tion." 



The following are two of his experiments : 



1st. The sensitive paper was partly covered by glass plate, in contact with 

 it; another plate, of glass or iA r ory, was placed across the first, so as to oppose 

 the direct radiation from the part which covered it, but not to the circulation 

 of any vapors emanated; when the box was opened, the paper was found 

 evenl}' blackened throughout, except under the glass in contact with the 

 paper. 



2d. The box containing the insolated sheet was left for four hours in a 

 warm place. M. Laborde then opened it carefully, and, holding the opening 

 downwards, gently withdrew the sheet; then, quickly fixing the sensitive 

 paper upon the cork, he re-closed the box and placed it in a cool place. When 

 it was again opened, after twelve hours, the sensitive paper was found 

 blackened, notwithstanding the absence of the iusolated sheet. 



SOLAR LIGHT AXD HEAT. 



M. de Chacornac, after numerous observations, has arrived at the conclu- 

 sion that the central portion of the solar disc, equal to three-tenths of its 

 diameter, is the most brilliant; and that the luminosity gradually diminishes 

 from the edge of this space to the rim of the disc. Near its edge the light 

 is only half as brilliant as in the central space. 



M. Secchi has also made analogous discoveries with respect to the sun's 

 heat, and finds that the calorific power of the zone nearest the edge of the 

 disc is only half that of the centre. 



ON TIIE MEASUREMENT OF THE CHEMICAL ACTION OF THE SOLAR 



RAYS. 



In a recent lecture on the above subject before the Royal Institution, Lon- 



ssor Roscoe stated: That the heating rays of the solar spectrum 



slowly, and are situated near the red end; while at the violet 



the most rapidly vibrating or chemical rays, by whose agency 



