28 THE AMEEICAN MONTHLY [February, 



good. The heavy, stiff' abominations, sometimes furnished with even 

 high-priced instruments, ought not to be tolerated by any buyer. A 

 gLass sHding stage, of simple construction, is a real convenience, much 

 said to the contrary notwithstanding. One can make with its aid the mi- 

 nute movements often required with greater ease and certainty, especially 

 with one hand, than by manipulating the slide itself. But I should 

 make this so that it can be instantly removed or left ofi' altogether if 

 the buyer so preferred. A mechanical stage need only be used in 

 special work, but cfs it is essential in photography with high -power ob- 

 jectives, and in work requiring much careful searching of a field where 

 only high powers suffice, it is desirable to have it possible to readily 

 attach the mechanism to the common stage. I prefer the form by which 

 the 3X1 inch slide is simply grasped at the ends, allowing it to lie flat 

 on the surface of the plain stage ; the preference is mainly from the 

 simplicity and cheapness. But a mechanical stage is a delusion, an in- 

 tolerable vexation, if the movements are not smooth and under exact 

 and easy control. Better have none at all than one that jumps, now 

 refuses to go, and now goes too far. If worth having, it is worth 

 graduating to facilitate refinding a desired object. In any event, it must 

 be easily removable, leaving the plain stage readily accessible. 



The arm (Jackson model) must support the tube along the side, and 

 should be so fashioned as to make a convenient handle, by which the in- 

 strument is grasped when moved. This last is a very minor consider- 

 ation, but really worth attention. For myself, I should prefer to have 

 this also of japanned iron, gracefully curved and rounded. Here espe- 

 cially, sharp angles, the pride of brass-filers, are objectionable in use, 

 and are exceedingly liable to become the worse in appearance from wear. 

 The fine adjustment must be thoroughly perfect in action. This must 

 be made emphatic beyond everything else. The movement must be 

 easy, absolutely prompt, rigidly free from lateral displacement, and with 

 as much range as possible ; in any case not less than an eighth of an 

 inch. The position of the milled head controlling the screw is a mat- 

 ter of much more moment than commonly thought. It is more essen- 

 tial that this be low than it is that the stage be so placed. To reach up 

 under one's chin for the milled head is annoying. The less the dis- 

 tance from the stage to the milled head of the fine adjustment the better, 

 for the hand is so frequently passed from one to the other that no ob- 

 stacle should be permitted to interfere with the movement. This milled 

 head must be equally accessible to either hand, and in every way the 

 most conveniently handled of any part of the instrument. It should 

 also be graduated with degree marks, though it cannot be said to be 

 essential that these should be numbered. The motion must apply to 

 the whole tube. Nothing else can be considered ideal, whatever may 

 be said of nose-pieces and stage movements. 



A rack and pinion, or something equally good, should be considered 

 essential for the coarse adjustment. To be sure, one can manage a tube 

 slipping in a sleeve ; but I will stick to the rack and pinion with two 

 good-sized milled heads, unless something better is offered. With good 

 workmanship this movement is perfectly smooth, with no back-lash. 

 Oblique teeth, used by some manufacturers, seem to be advantageous. 

 We come now to the mooted question of the size and length of the 

 tube. There are two advantages of the larger tubes which must be 



