552 



Transactions of the Society. 



filar micrometer in which the movable lines cross at an acute 

 angle. 



With the Zeiss -Vim and Zeiss filar micrometer, one division 

 of the micrometer = 0-01247 /u,. Eook W, pp. 82-4. 



SERIES C. 



r = +1*6 div. = 

 r = + 0*5 div. = 



Average deviation from mean = 

 Greatest deviation from mean = 



+ 0-02 fi 

 + 0-006 fi 



1 • 7 div. = • 02 fi. 

 4-6 div. = 0-06 ft. 



SERIES D. 



r = ± 1 • 9 div. = 

 r o — +0-6 div. = 



Average deviation from mean = 

 Greatest deviation from mean = 



