Comparative Micrometric Measurements. By M. D. Ewell. 551 



SERIES A. 



r = + 1 • 2 div. 

 r = +0-4 div. 



Average deviation from mean 

 Greatest deviation from mean 



± • 02 fi 

 ± 0-006 yu. 



: 1-4 div. = 0-02 fM. 

 3-1 div. = 0-05 ix. 



SERIES B. 



Same Squared 



2 ] = 136-5 



r = + 2 • 6 div. = 

 r = +0-8 div. = 



Average deviation from mean = 

 Greatest deviation from mean = 



± 0-04 /a 



+ 0-01 LI 



3 • 2 div. = 0-05/i. 

 6-8 div. = 0-10/t. 



In the measurements with the Zeiss T Vim objective the mag- 

 nified image of the lines of the stage micrometer completely filled 

 the space between the two parallel spider lines, so that it was not 

 easy to set on the lines. The following series were therefore made 

 with the same objective, using instead of the Gaertner filar, a Zeiss 



