recur farther on, and reported in favor of the adoption 

 of two standards for tube length, viz., short standard 

 1 60.0 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. There are no optical advant- 

 ages in the one or the other. The short length is 

 almost a necessity, however, in the Continental pattern 

 of microscopes as compactness is the special desidera- 

 tum; but, while this subject will be given more extended 

 attention and optically considered farther on, it might 

 be stated here that when an objective, except perhaps 

 in the very low powers, is constructed to be used with 

 a certain length of tube, it should be used with this 

 length only. This statement cannot be made too 

 prominent and will bear repetition. 



Stage. This should be of such strength that, under 

 considerable magnification, the object may be moved 

 in different directions without displacement of focus. 

 This depends upon the matei ial of which it is made, 

 its thickness, and the strength of attachment between 

 it and the arm. Absolute ligidity is practically impos- 

 sible when considerable force is exerted, as can easily 

 be determined in the best instruments, and it is a 

 mistake to condemn an instrument for this cause as is 

 sometimes done. If the object will remain in fociis 

 under a high power with a fair amount of pressure 



37 



