262 THE HISTORY AJND DEVELOPMENT OF THE MICEOSCOPE 



parts of. -i microscope will commend itself to all workers of large and 

 broad experience : 



1. A coarse adjust incut by rack and pinion. 



2. A -ub stage. 



3. A fine adjustment. 



4. Mechanical movements t<> sub-stage, i.e. focussing and centring. 

 ."">. Mechanical stage. 



I). Kack-wnrk to dra\v-tul)e. 



7. Finder to stage. 



X. Plain rotary stage. 



'.I. <; rad nation and rack -work to rotary stage. 



10. Fine adjustment to sub-stage. 



1 1 . Rotary sub-stage. 



]'2. Centring to rotary stage. 



This table gives in. order the relative values of the several parts ; 

 thus a microscope with a rack-and-pinion coarse adjustment and a 

 sub-stage is to be preferred before a microscope witli a rack-and- 

 pinion coarse adjustment, -A fine adjustment, but no sl>-xt<i</<'. Or a 

 microscope with a coarse adjustment by rack and pinion, a sub-sta^v. 

 and a fine adjustment, is to be preferred before one with the same 

 coarse adjustment and a mechanical stage movement, but no sub- 

 stage or fine adjustment : and so on. The last item is of least 

 importance, and the importance of all the others is in the order of 

 their numeration. 



A i Hither matter of some significance to the tyro is the relative 

 value, from the point of view of time consumed, and therefore of 

 I'rinie cost, in producing the several kinds of microscopes. The 

 No. 1 stands of li.-ilf a dozen makers may be near the same cost, but 

 nia\ nevertheless have involved the consumption of very different 

 <liianiities of the highot class of skilled labour in their production. 



.Manifestly the first thing to be lookedat in a microscope making 

 any pretensions to i|uality is the character of the workmanship ; and 

 this should carry with it the question how much machine, and how 

 much hand \\ork mid fitting there is in it. Arcs graduated on 

 silver, tor example, are very attractive, and with many are most 

 impressive; but. thev are simplv machine work, and quite inex- 

 pensive. 



In the two great, types of models, the liar movement and the 

 Jackson limb, the bar movement involves more than double the 

 actual hand-fitting; while a line adjustment with a movable iiose- 

 piece takes twice the lilting of one in which the whole body is moved 

 by the line adjust incut screw. I n the same way a -mechanical xtayK 

 which is made of machine-planed plates, sliding in a machine-ploughed 

 groove, is much less costly in t hue and quality of la hour than a hand- 

 made sprung stage. So a Nnl>-xlti</<' having a movable ring pressed 

 by tuo screws against a .spring has very far less work, and work of 

 a louer class, than one with .1 true rectangular centring movement. 



It will follow, then, thai a .lackson limbed microscope with no 

 movable nose-piece, with a machine made mechanical stage and a 



movable ring for sub-stage, \\ill not have involved more, perhaps, 



than a t hi i (1 of ) |u> skilled work which must lie e\| ended on a well- 



