190 EWELL-STUDY OF MODERN MICROMETERS. [April, 19, 



The last two scales (IX and X) were ruled from 20 to 25 years 

 ago and are included in this list simply for the purpose of compari- 

 son with more recent productions. 



The results above given need no comment and show that no 

 advance in precision has been made in the last twenty-five years; 

 indeed the results do not seem to equal those of the former period. 



Chicago, April 15, 1907. 



