NATURAL PHILOSOPHY. 159 



noon ; this was observed at a very early period by Daguerre. For 

 drawings by application, this is but slightly, if at all, felt, but with the 

 camera it is of some consequence to attend to this fact. We are not 

 yet in a position to record more than the fact the cause of the dif- 

 ference is not yet determined ; probably it may be found to exist in a 

 greater absorptive action of the atmosphere, caused by the elevation 

 of aqueous vapor from the earth. But the experiments of M. Mala- 

 guti seem to imply the contrary, this philosopher having found that 

 the chemical rays permeate water more readily than they do air; 

 some experiments of my own, however, are not in accordance with 

 M. Malaguti's results.. In the neighborhood of large towns it might 

 be accounted for by the circumstance of the air becoming, during the 

 day, more and more impregnated with coal smoke, &c., which offers 

 very powerful interruption to the free passage of the chemical rays. 

 This will, however, scarcely account for the same interference being 

 found to exist in the open country, some miles from any town. Until 

 our meteorological observers adopt a system of registering the varia- 

 tions of light and actinic power by means of some well devised instru- 

 ment, we cannot expect to arrive at any very definite results." 



IMPROVEMENTS IN PHOTOGRAPHY. 



PHOTOGRAPHY has made rapid progress during the last two years, 

 especially in the mode of operating on paper and glass. To M. 2s iepce 

 must be accorded the merit of having contributed to the perfecting of 

 this art, by his beautiful discovery of the process of albumen on glass. 

 Proofs have been obtained by this means, which, for beauty of design, 

 clearness and fineness of detail, leave nothing to be desired. There 

 are, however, serious inconveniences attendant upon this process. 

 The length of exposure in the camera necessary for obtaining an 

 image, has hitherto compelled us to limit its application to landscapes 

 and architecture, and renounce its employment in portraiture. These 

 difficulties have at last been overcome by Mr. Bingham, of London, 

 who substitutes a layer of collodion instead of the albumen of M. 

 Niepce. This process, it is stated, rivals in beauty the albumenized 

 plate, and even surpasses the daguerreotype in sensibility to light. 

 The manner of operating with collodion resembles, in many respects, 

 the albumen process, and no operator accustomed to the manipulations 

 of the albumen on glass, can fail to succeed with collodion. The 

 details of the process are described at length by Mr. Bingham, in the 

 Comptes Rendus of May, 1852, and in the London Chemist for July, 

 1852. 



Photographs on Glass. According to a process described by M. 

 Pucker, in the Arcli'w der Phann. Ixix., a thin film of iodide of sul- 

 phur is formed upon plate glass, by covering the glass, which must be 

 perfectly clean, with a very thin coating of sulphur, and then impreg- 

 nating this" for a few seconds with the vapor of iodine. The glass 

 plate is then placed in the camera, where at the same time the vapor 

 of some quicksilver in an iron cup in the bottom of the camera, acts 



