Royal Society^ 69 



of photography are not mainly dependent upon a separate agent 

 accompanying light, rather than upon light itself. It is, indeed, dif- 

 ficult not to believe that a picture, taken in the focus of the camera 

 obscura, and which represents to the eye all the gradations of light 

 and shade shown by the original luminous image, is not an effect of 

 light ; certain it is, however, that the different coloured rays exer- 

 cise different actions upon various chemical compounds, and that 

 the effects on many, perhaps on most of them, are not proportionate 

 in intensity to the effects upon the visual organs ; those effects, 

 however, appear to be more of degree than of specific difference, 

 and without pronouncing myself positively upon the question, hitherto 

 so little examined, I think it will be safer to regard the action on 

 photographic compounds as resulting from a function of light : so 

 viewing it, we get light as an initiating force, capable of producing, 

 mediately or immediately, the other modes of force. Thus, it imme- 

 diately produces chemical action ; and having this, we at once ac- 

 quire a means of producing the others." 



Mr. Grove then relates the following beautiful experiment, by 

 which he conceives th.it he showed the production of all the other 

 modes of force by light : — " A prepared Daguerreotype plate is in- 

 closed in a box filled with water, having a glass front, with a shutter 

 over it ; between this glass and the plate, is a gridiron of silver wire ; 

 the plate is connected with one extremity of a galvanometer coil, 

 and the gridiron of wire with one extremity of a Breguet's helix ; 

 the other extremities of the galvanometer and helix are connected 

 by a wire, and the needles brought to zero. As soon as a beam of 

 either daylight or the oxyhydrogen-light is, by raising the shutter, 

 permitted to impinge upon the plate, the needles are deflected : thus 

 light being the initiating force, we get chemical action on the plate, 

 electricity circulating through the wires, magnetism in the coil, heat 

 in the helix, and motion in the needles." 



We have had some difficulty in selecting passages for quotation 

 from this publication, on account of the profusion of interesting 

 matter which it contains, though in so small a space ; we believe, 

 however, that the selections which we have given are such as will 

 well and sufficiently illustrate the interesting views of their author. 



XII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from vol. xxx. p. 207.] 

 Feb. 11, "/^N the Amount of the Radiation of Heat, at night, 

 184'7. ^^ from the Earth, and from various Bodies placed on, 

 or near the surface of the Earth." By James Glaisher, Esq. Com- 

 municated by G. B. Airy, Esq., F.R.S., Astronomer Royal, &c. 



The author enters into a very detailed description of the construc- 

 tion of the thermometers he employed in these observations, and 

 the precautions he took to ensure their accuracy ; and gives tabular 

 records of an extensive series of observations, amounting to a num-» 



