RJCHARD RAi 



M E M O i R S 



NATIONAL ACADEMY OF SCIENCES, 



V o 1 11 111 e ^^ T T I 



SEVENTH MEMOIR. 



WASHINGTON: " 



(i O V E K N M E N T P K IN T I N G O Y'V 1 C K 

 1 !♦ 2 . 



