NATURAL PHILOSOPHY. 149 



gated, and too broad for the nicer purpose of measurement. This 

 apparent enlargement of the disk we attribute, in a great measure, to 

 two causes. One is the variable nature of atmospheric refraction, 

 when influenced by sudden changes of temperature. This trouble we 

 hope to get rid of by increasing the sensitiveness of the surface receiv- 

 ing the impression. The other operation will then require less time, 

 and, of consequence, be subject to fewer and less extensive vibrations. 

 The other difficulty to be overcome is the irregular motion of the ma- 

 chinery winch carries the telescope. Although the machinery at 

 present attached to the telescope is the best that German ingenuity 

 could devise, and answers a tolerably good purpose on ordinary occa- 

 sions, yet it is deficient for our nicer operations. The telescope 

 should, during the nicer process, be propelled with a uniform sidereal 

 motion, in order that the successive rays from the star may fall on 

 precisely the same part of the plate which is to receive the impres- 

 sion. If this be not the case, the image will be deficient in distinct- 

 ness of outline, and unduly enlarged. To effect this, we intend to 

 apply to our great equatorial a machine which we have devised for 

 the purpose of producing uniform rotary motion. It is our purpose to 

 pursue the subject of I)aguerreotyping the stars, proceeding step by 

 step from the brighter to those of lesser magnitude. We do not de- 

 spair of obtaining, ultimately, faithful pictures of clusters of stars, and 

 even nebulae." 



The Daguerreotyping of stars and nebulas was first accomplished by 

 some Roman astronomers, among whom M. Rondoni has been espe- 

 cially successful.* 



PHOTOGRAPHY ON GLASS. 



THE following new process for obtaining photographic pictures 

 upon glass is communicated to the London Atherueum for June, by 

 Mr. T. A. Malone : To the white of an egg add its own bulk of 



o o 



water, and after the two are \vell mixed, strain the solution. A piece 

 of plate-glass, thick or thin, is then properly cleaned, and afterwards 

 coated with the albumen, which forms a film upon the glass so thin 

 and transparent that the brilliancy of the glass'is unimpaired ; indeed, 

 it is almost necessary to mark it, to know which side has been coated. 

 The plate is then coated with iodine, and afterwards rapidly immersed 

 in a solution of aceto-nitrate of silver. Allow it to remain until the 

 transparent yellow tint disappears, to be succeeded by the milky-look- 

 in"' film of iodide of silver. After washing with distilled water, the 



O cj f 



plate is ready for the camera. After it has been submitted to the 

 action of the light, pour over its surface a saturated solution of gallic 

 acid. A negative Talbotype image on albumen is the result. Wash- 

 ing with a solution of hyposulphite of soda, until the yellow tint is re- 

 moved from the shadows, completes the process. 



But where is the novelty? Let us go back a step. While the 

 gallic acid is developing its reddish-brown image, pour upon the sur- 



* Fee Annual of Scientific Discovery, 1850, p. 111. 

 13* 



