MEMOIRS AMERICAN ACADEMY. VOL. XIII. 
PLATE XX\i 
MAGNESIUM 
* 
t 
FIG. 9 (NEGATIVE) 
SOLAR 
'■ 
F!G. 10 (NEGATIVE) 
CALCIUM 
SOLAR 
F ,G. II (NEGATIVE) 
TROWBRIDGE. -HIGH ELECTROMOTIVE FORCE 
