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At the last meeting of the American Society of 

 Microscopists a committee was appointed to consider 

 the tube lengths as well as other subjects to be men- 

 tioned hereafter and reported in favor of the adoption 

 of two standards for tube lengths, 160.0 mm., or 6.3 

 inch for the short one, and 8| inch, or 216.0 mm., 

 for the long one. The American makers have 

 adopted these two lengths and we believe are gen- 

 erally following them. Practically, there are no 

 advantages in one or the other, except, perhaps, in 

 so far as the short tube might be considered advan- 

 tageous, but optically this recommendation of the 

 committee is far reaching, because an objective, par- 

 ticularly in giving considerable magnification, when 

 constructed to be used with a certain tube-length, 

 should be used with it only. When used with the 

 other standard it will fail to give satisfactory results. 

 This subject, with the optical results, will be touched 

 upon again later on. 



Mechanical Parts As there will be but little 

 occasion to recur to the mechanical portions of the 

 microscope, we take the occasion to speak of them 

 in a more extended way in this connection. 



Stage. This may be divided into three classes, 

 ordinary, semi-mechanical, and mechanical. 



The first consists of a plain plate, either round or 

 square, on which the slide is held by means of the 

 clips. As the microscope is used principally in an 

 inclined position, the pressure exerted by the clips 



