Chemistry and Physics. 307 
sin inf, or if 7 is small, yd. The motion of the beam is double 
this, and the reflected ray travels twice as rapidly as the mirror; 
hence calling » and n’ the two readings, and J the distance of the 
scale, we have pala" 1. If the four points do not lie in one 
plane a correction is readily applied. Comparing the results, he 
concludes that while this instrument is very easily made and abso- 
ute measures readily obtained within a tenth of a per cent, it com- 
Fe, Co, Ni, 
Mn, Ce, U, Cr, Ba, Sr, Ca, K, Al, representing 416 lines.— Nature, 
238, Ec 
. 
ave any other origin than elective atmospheric absorption.— 
ure, 278. B. 0, P. 
