LENS-HOLDERS 25 1 



portability may be altogether sacrificed, and the instrument is to be 

 adapted to the making of large dissections under a low magnifying 

 power, some such form as is represented in fig. 203 constructed by 

 Messrs. Baker, on the basis of that devised by Professor Huxley for 

 the use of his Practical Class at South Kensington, will be found 

 decidedly preferable. The framework of the instrument is solidly 

 constructed in mahogany, all its surfaces being blackened, and is so 

 arranged as to give two uprights for the support of the stage and 

 two oblique rests for the hands. Close to the summit of each of these 

 uprights is a groove into which the stage-plate slides ; and this may 

 be either a square of moderately thick glass or a plate of ebonite, 

 having a central perforation into which a disc of the same material 

 may be fitted, so as to lie flush with its surface, one of these being 

 readily substituted for the other, as may best suit the use to be 



FIG. 202. Zeiss's lens-holder. 



made of it. The lens is carried on an arm working on a racked 

 stem, which is raised or lowered by a milled-head pinion attached to 

 a pillar at the further right-hand corner of the stage. The length 

 of the rack is sufficient to allow the arm to be adjusted to any 

 focal distance between 2 inches and J inch. But as the height of 

 the pillar is not sufficient to allow the use of a lens of 3 inches 

 focus (which is very useful for large dissections), the arm carrying 

 the lenses is made with a double bend, which, when its position is 

 reversed, as in the dotted outline (which is readily done by unscrew- 

 ing the milled head that attaches it to the top of the racked stem), 

 gives the additional inch required. As in the Quekett micro- 

 scope, a compound body may be easily fitted, if desired, to a separate 

 arm capable of being pivoted on the same stem. The mirror frame 



