174 ANNUAL OF SCIENTIFIC DISCOVERY. 



a photographic telescope has been ordered for the Kew Observatory. The 

 proportions of the instrument, which is nearly completed, are as follows : 

 The diameter of the object-glass is 34 inches, and its focal length 50 inches ; 

 the image of the sun will be 0-465 inch, but the proposed eye-piece will, with 

 a magnifying power of 2 5 '8 times and focal length cc, increase the image to 

 12 inches, the angle of the picture being about 13 45'. The object-glass is 

 under-corrected in such a manner as to produce the best practical coincidence 

 of the chemical and visual foci. Other arrangements have been made with 

 great care and accuracy for regulating the light, the time of producing the 

 image, and for measuring the diameter of the spots, etc. 



PRINTING ON CLOTH BY THE PHOTOGRAPHIC PROCESS. 



The following method for printing designs on cloth by means of photography 

 has been invented, and to some extent introduced in France. The cloth to be 

 printed, or figured on, is first plunged into a chemical solution, and then dried 

 in the dark : it thus becomes sensible to the action of the light. It is then 

 exposed to the light, in the presence of the object to be reproduced, and when 

 it has been submitted to the action of the solar rays, it is subjected to a solu- 

 tion which develops the colors and renders them permanent. This is the 

 operation for fixing the colors, after which the material is washed. The print, 

 ing machine is composed of a simple rectangular frame, mounted on four feet. 

 The frame has on one side a flexible bar, and on this bar is rolled the cloth 

 which is to be printed, properly prepared. From thence the cloth goes over 

 the table and passes under a pane of glass, on which, by maans of a combina- 

 tion of opaque or transparent objects, pieces of paper, for example, any design 

 which is to be produced is figured. All the part of the cloth which is to be 

 covered by the square remains under it the time necessary to subject it to the 

 chemical action of the light, and it will be understood that this action is only 

 exercised on those parts of the cloth which remain exposed to the solar rays. 

 Those which are shaded are of course preserved. While this exposure lasts, 

 the cloth remains in contact with the under side of the glass. This contact is 

 procured in the following manner : The portion of the cloth exposed rests on a 

 cushion composed of a pine board and several thicknesses of flannel, and two 

 springs, one on each side, press the cushion against the glass. 



As soon as the chemical action has been effected, which is discovered by the 

 exposed surface becoming white or brown, according to the preparation which 

 has been used, the workmen lower the cushion by aid of a lever, the cloth 

 becomes free, and a new portion of it takes the place of the square of the one 

 which was previously there, the first going on to be subjected to the fixing 

 operation. For this purpose the last is carried by two rollers (rouleaux de guides) 

 under the same table, where there is a trough containing the solution which is 

 to develop the impression. The piece is drawn through by a couple of cylinders 

 forming a roller, which are turned with a crank by a man, as soon as he has 

 lowered the cushion which has just been mentioned. The setting the color is 

 now done, and the cloth must be washed. This takes place immediately, the 

 cylinders forming a roller, and depositing them in a tub filled with water. 



