478 SUMMARY OF CURRENT RESEARCHES RELATING TO 



is no means but tliat of the finger to bring it back again. Of course, by 

 keeping tho slido pressed against the stud one can regulate the motion 

 backwards by means of tho screw. If a horizontal backward motion is 

 required, thoro are two — and only two — alternatives before you : either 

 you must clip the 6iide, or you must place the slide in a moving plate. 

 If, on tho one hand, tho slido is clipped, you fall into the errors 

 mentioned above ; and if, on the other, you adopt tho moving plate, you 

 must, if it is to stand a crucial test, copy the Powell model. Now, as 

 tho scope of the new stage is to improve tho student's Microscope at a 

 small extra cost, it stands to reason that tho second alternative is out of 

 tho question. 



The advantages I claim for the new movement aro as follows : — 



(1) The vertical and horizontal movements are independent of one 

 another, so you can have a vertical movement fitted to your Microscope 

 without the horizontal, or vice versa. 



(2) By removing the screws in the blocks which arc the only things 

 above tho stage, the stage is left perfectly plain, just as if there was no 

 mechanical movement at all. 



(3) By merely slotting tho sliding-bar, to enable it to pass over the 

 screw-heads, tho sliding-bar and the mechanical movement can be used 

 independently of one another. 



(4) By screwing a bar to the blocks you have a perfect mechanical 

 vertical movement. This, I think, in practice, will bo found the most 

 useful. 



(5) By graduating the heads of the pinions, and by marking the 

 stage for each complete revolution, a finder and a rough micrometer 

 sufficiently accurate for low and medium powers is made. 



(6^ It is inexpensive. 



(7) And perhaps the most important. The moving pinions being 

 fastened to a fixed stage, and tho blocks sliding in grooves in the stage, 

 renders the movement peculiarly steady." 



When exhibited it was pointed out * that as both hands are required 

 to work the stage — one for the milled head and the other to keep the 

 slide pressed against the screws — the great advantage of a mechanical 

 stage, in being able to focus at the same time that the slide is moved, 

 was lost.f 



Fine-adjustment by tilting the Stage. — In describing Queen and 

 Co.'s " New Laboratory Microscope, Acme No. 5," in which the upper 

 stage-plate is lifted at one end by a screw, the writer says J that this 

 " plan of constructing tho fine-adjustment has the following invaluable 

 features, which especially fit it for class work in the laboratory. 



First (and principally). Perfection of action : The upper plate, 

 carrying the object, must respond instantly to the movement of the screw 

 — upward by positive action, downward by the spring of the plate ; and 

 without any lateral or side motion ; these, of course, aro tho essential 

 features of a good fine-adjustment. 



Second (and important). This perfect action will continue as at first ; 

 as there are no joints to wear looso or become strained, there can he 

 developed no lost motion nor lateral motion by wear or rough handling, 

 all being made practically in one solid piece. 



* Ante, p. 334. t Cf. Engl. Mech., xlvii. (1888) p. 117. 



% Queen's Micr. Bulletin, iv. (1887) p. 11 (I pL). 



