NATURAL PHILOSOPHY. 151 



which the civilized world will deplore, the loss of that sight which 

 has detected so many brilliant phenomena and penetrated so deeply the 

 mysteries of the material world, he is now completing, with the aid 

 of other eyes than his own, those splendid researches which will im- 

 mortalize his own name and add to the scientific glory of his country. 



Sir David Brcwster's Address, British Association. 



Among the discoveries in photography during the past year, the 

 most prominent, perhaps, are those patented by Messrs. Talbot and 

 Malone of England. The points embraced in their specification are : 



1. The use of plates of unglazed porcelain, to receive the photo- 

 graphic image. 2. A method of converting or changing negative 

 photographic images into positive ones. 3. The employment of the 

 vapors of iodine and bromine in photography, as a preliminary to the 

 formation of images upon films of albumen, gelatine, or other sub- 

 stances of animal or vegetable origin, the employment of these vapors 

 having been hitherto confined to their action on polished metallic sur- 

 faces. 4. A method of obtaining more complete fixation of photo- 

 graphic pictures on paper. 5. The use of varnished paper, or other 

 transparent paper impervious to water, as a substitute for glass, in 

 certain circumstances, to support a film of albumen, for photographic 

 purposes. 6. Forming pictures or images on the surface of polished 

 steel plates. 



A communication to the French Academy by M. Evrard presents 

 some additional facts. The great desideratum to be obtained in pho- 

 tography is a method of rendering the exercise of the art on paper 

 at once simple, certain, and easy. To accomplish this he describes, 



1. A method of taking photographic sketches on dry paper, in place 

 of the damped paper, as in the processes at present in use, thus re- 

 moving the difficulties arising from the necessity of preparing the pho- 

 tographic paper at the place where it is required to be used. 2. A 

 simple method of preparing this photogenic paper, so that it may be 

 prepared and sold ready for the use of the amateur, who need not 

 henceforth take the trouble of preparing it himself. 



In another paper, M. Evrard details his method of obtaining the in- 

 stantaneous formation of the image in the camera obscura. Fluoride 

 of potassium, added to iodide of potassium, in the preparation of the 

 negative proof, produces instantaneous images on exposure in the cam- 

 era. To assure myself of the extreme sensibility of the fluoride, I 

 have made some experiments on the slowest preparation employed in 

 photography, that of plates of glass covered with albumen and iodide 

 of potassium, requiring an exposure at least sixty times longer than 

 the same preparation on paper. On adding the fluoride to albumen 

 and iodide of potassium, and substituting for the washing of the glass 

 in distilled water, after treatment with the aceto-nitrate of silver, a 

 washing in fluoride of potassium, I have obtained the image immedi- 

 ately on exposure in the camera. This property of fluoride of potas- 

 sium is calculated to give very valuable results, and will probably 

 car.ce, in this branch of photographic art, a change as radical as 

 that effected by the use of bromine on the iodized silver plates of 

 M. Daguerre. 



