SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



PART OF VOLUME XXXIV 



On the Construction of a Silvered Glass 

 Telescope, Fifteen and a Half Inches 

 IN Aperture, and its Use in Celes- 

 tial Photography 



By henry draper, M.D. 



PROFESSOR OF NATURAL SCIENCE IN THE UNIVERSITY OF NEW YORK 

 (Reprinted from VoL XIV', " Smithsonian Contributions to Knowledge," 1864) 



AND 



On the Modern Reflecting Telescope 



and the Making and Testing 



OF Optical Mirrors 



By GEORGE W. RITCHEY 



ASSISTANT PROFESSOR OF PRACTICAL ASTRONOMY, AND SUPERINTENDENT OF 

 INSTRUMENT CONSTRUCTION, IN YERKES OBSERVATORY 



,iNc/f^; 







v^ 





m 



(No. 1459) 



CITY^ OF WASHINGTON 

 PUBLISHED BY THE SMITHSONIAN INSTITUTION 



1904 



