SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE. 

 180 



ON THE CONSTRUCTION 



or 4 



SILVERED GLASS TELESCOPE, 



FIFTEEN AND A HALF INCHES IN APERTURE, 



AM> 



ITS USE IN CELESTIAL PHOTOGRAPHY. 



BY 



HENRY DRAPER, M.D., 



PBOFB880B OP NATURAL SCIENCE III TUB UNIVERSITY UP NEW YORK. 



[ACCEPTED FOB PCBLIOATIOK, JANUABY, 1864.] 



