"KNOWLEDGE" 



ROUGH WAYS MADE SMOOTH 



A SERIES OF 



familiar fesags on Scientific Subjects 



BY 



RICHARD A. PROCTOR 

 i> 



AUTHOR OF 



MYTHS AND MARVELS OF ASTRONOMY* 'PLEASANT WAYS IN SCIENCE' 



'SCIENCE BYWAYS' 'THE BORDERLAND OF SCIENCE ' AND 



'LIGHT SCIENCE FOR LEISURE HOURS' 



NEW EDITION 



LONDON 

 LONGMANS, GREEN, AND CO. 



AND NEW YORK : 15 EAST i6' h STREET 

 1888 



All rights reserved 



