Comparative Micrometric Measurements. By 31. D. Ewell. 549 



With this combination one division of the micrometer equals 

 • 10175 jj,. Every measurement was made upon the first T \q mm. 

 of " Powell and Lealand No. VIII.," Book W, p. 79. 



r = + • -4 div. = +0-04/1 

 r = ±0-1 div. = +0-01/1 



Average deviation from mean without regard to sign = 0-46 

 div. = 0-05/i. 



Greatest deviation from mean = 1-2 div. = 0*12 fi. 



The same instruments, except No. 5 Leitz objective, one division 

 = O-067/i. Book W, p. 79. 



r = + 0-44 div. = ± 0-03 /i 

 r = + 0-14 div. = +0-01/1 



Average deviation from mean =0-5 div. = • 03 /i. 

 Greatest deviation from mean = 1*3 div. = 0-09 /i. 



The same instruments, except 4 mm. Spencer objective ; une 

 division equals ■ 04725 /i. Book W, p. 80. 



