M. TECHNOLOGY. .529 



ing upon the plate may be greatly facilitated by the use of 

 photography. It will be readily understood that the object 

 of the silver coating is to secure a perfectly sharp and dis- 

 tinct outline after the etching has been accomplished. 6 B, 

 June 1, 1874, 153G. 



DIRECT PHOTOGRAPHY OF THE SOLAR PROTUBERANCES. 



Professor Sellack, of Cordoba, who has the use of a 13-inch 

 photographic objective, narrates his experience in attempt- 

 ing the photography of solar protuberances by means of the 

 spectral line H. Gamma. According to him, a thin layer of 

 iodide of silver upon a plate of glass absorbs all the violet 

 light of the spectrum, and he therefore proposes to cover 

 the surface of his lens with a thin layer of this substance. 

 By means of the light that is then transmitted he would di- 

 rectly photograph the solar protuberances. His first at- 

 tempts, for many reasons, have been quite unsatisfactory; 

 but the suggestion seems worthy of further development by 

 those spectroscopists who have greater conveniences at their 

 command. Astron. JVachric/Uen, LXXXIV., 90. 



PREPARATION OF PHOTOGRAPHIC DRY PLATES BY DAYLIGHT. 



The following process, suggested by Professor Himes, for 

 the preparation of photographic dry plates, renders unneces- 

 sary the prolonged, unpleasant, and unhealthy confinement 

 to the damp, dark room, and in a great measure lessens the 

 liability to accidental stains on the plates. It rests upon 

 the fact, ascertained by him, that at least any effect capable 

 of development of light upon iodide or bromide of silver 

 may be removed and further action of light prevented by 

 the application of a solution of iodide of potassium, or of 

 similar substances, or even by prolonged action of sunlight 

 alone; but that these silver salts may again be rendered 

 sensitive to light by treating them with a solution of tannin 

 or of nitrate of silver, or by exposing them to fumes of am- 

 monia. Glass plates, therefore, coated with the usual bromo- 

 iodized collodion, are plunged in the nitrate-of-silver bath 

 in an ordinary well-lighted room; the excess of nitrate of 

 silver is rinsed off with water, and about a five-per-cent. so- 

 lution of iodide of potassium is allowed to flow over them; 

 they are again rinsed, and finally allowed to dry. Or the 



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