it^ Intelligence and Miscellaneous Articles. 



al90,t:k)|e ftpcelerating influence of the ammouia seems to be retained 

 in the camera for a considerable time, notwithstanding its volatility ; 

 in fact I have sometimes thought its presence in the operating room 

 alone had an accelerating influence, and am persuaded it will be 

 highly advantageous in a room where bromine or iodine is evolved, 

 •whose presence is known to suspend the action of light altogether; 

 this vapour, on the contrary, neutralizes them, and instead of retard^ 

 ing the process, hastens it. 



I have not had time to institute further experiments, which I think 

 the subject well worthy of. My object now is simply to direct the 

 attention of photographists and the scientific world to the facti and 

 I shall be much mistaken if this compound of hydrogen and nitrogeij 

 4oes not prove a valuable adjunct to the photographic art, ^ ^„^^ ^oq 



I am, Gentlemen, . as ion m^ 



26 Tavistock Place, Tavistock S^— YjMir most obedient Servant, 



October 20, 1845. iTAvaaaao JAOi W. H. Hetsvett. 



P.S. I should add that my experiments were made with two me- 

 niscus lenses of smaljk aperture in front, and worked at the chemical, 

 not the visuali focus/with achromatic glas^s. I have no doubt much 

 ipore §atis£^ory.J%suits-iaay. be obtained.]^ - . .-■— •.>- 



: aiaworiz rijiv/ teuoiaiaiod xt-jf .8 1 aOTSJziod : niei . ^ 



: Jafioiavo vbgnsCt .IS .idr". -uoisisioa .r 



QJ%inripiV}l««mp«l» Of mines by MRA^B^,mj THE ELECTRIC 



'.i3e;i,AMPV (Letter of M. De la Rive to M, Boussingault.) 



Jriaii — . ■» 



■lU see, by the Compte Rendu des Stances de VAcademie, that you are 



engaged in seeking means to employ the voltaic pile in lighting 

 mines. This subject has also occupied my attention for a long time. 

 I have made several attempts, which have not been all equally fortu- 

 nate ; but I have lately had more success, and am now engaged in 

 maturing a process which I think is both ceconomical and convenient. 

 The pile which I employ is formed of several concentric cylinders, 

 of copper ox platinum, separated from one another by porous cylin- 

 ders, so as to form four or five pairs in a series ; the positive metal 

 is a liquid amalgam of zinc, or stUl better, an amalgam of potassium ; 

 the liquid is a solution of sulphate of copper, in case the negative 

 metal is copper, and of chloride of platinum when it is platinum. 



One of the chief difficulties is to maintain the light constant. In 

 this I have not yet perfectly succeeded ; but I have gained much by 

 employing small hollow thin cylinders of coke, analogous to those 

 employed in Bunsen's battery (except that their dimensions are 

 much less), and by arranging these cylinders as the wick of a lamp. 

 A ring or thick metallic disc, of the same diameter as the cyhnder 

 of coke, is arranged above the latter, so that the electric current 

 escapes between the two. Care must be taken that the current 

 pass from the coke cylinder, which is below, to the metallic con- 

 ductor, which is above, in order that the particles of carbon, trans- 

 ported from below up, fall by their own weight. The whole, that 

 is to say, the coke cylinder and the metaUic adjustments which 

 support it, as well as the ring or disc which serves as conductor, is 



