52 



being largely followed in America, the length is 

 from 8J to 10 inches (216.0 to 250.0 mm.) The 

 short tube of the European makers offers no 

 optical advantages, but is mainly used to contract 

 the height of the instrument to as great an extent 

 as possible, as this is the vital point throughout its 

 construction. 



Until recently this subject was given little atten- 

 tion, each maker following a standard which he 

 had adopted for himself. The pernicious influence 

 of this diversity was not appreciated by the public, 

 as it was not acquainted with the products of dif- 

 ferent makers, until Prof. S. H. Gage made it the 

 subject of a paper before the American Society of 

 Microscopists and as a result of his inquiries, 

 tabulated the standards as followed by the different 

 makers, which is published herewith. 



As a result of his reports a committee was 

 appointed to consider this subject, as well as that 

 of eyepiece, objective and thickness of cover glass, 

 to which we will recur farther on and reported in 

 favor of the adoption of two standards for tube 

 length. 



Short standard 160.0 mm. (6.3 inches) ; long 

 standard 216 mm. (8.5 inches) ; that the tube 

 length shall be considered those parts between the 

 upper end of the tube where the ocular is inserted 

 and the lower end of the tube where the objective 

 is inserted. While the European makers have paid 



