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NOTE. 



A Two-speed Fine Adjustment. 



By Edward M. Nelson. 



TO make use of a common but apt expression, we may say that 

 the two-speed fine adjustment has " come to stay." I have not 

 been able to hunt up back volumes to discover the first inventor 

 of a two-speed fine adjustment, but if we go back only as far as 

 1899, and turn up page 139 of the Journal for that year, we shall 

 find a new Microscope figured and described by Mr. Keith Lucas, 

 its designer. The principal novelty in this Microscope lies in the 

 peculiar form of its coarse and fine adjustments. Probably it 

 would be more accurate to describe this instrument as a Micro- 

 scope possessing a two-speed fine adjustment and no coarse adjust- 

 ment, and this is the exact point where this ingeniously designed 

 Microscope fails — it lacks a coarse adjustment, its so-called coarse 

 adjustment being in reality a quick fine adjustment. 



In 1901 we had three forms of two-speed fine adjustments 

 brought by Mr. Ashe to the notice of the Quekett Microscopical 

 Club. Two of these were of the differential screw type, and all of 

 them were very skilfully designed. Since then we have had a new 

 two-speed fine adjustment brought before us in the Males-Watson 

 Microscope, exhibited here at the June Meeting, 1902. This is 

 the only two-speed fine adjustment I have had the opportunity of 

 practically testing ; its performance was not only perfectly steady, 

 but it was prompt in its action as well. 



It would seem that the best kind of two-speed fine adjustment 

 will eventually settle down to some sort of combination of levers, 

 for an arrangement of screws working within screws will require 

 fine finish and careful adjustment if the movement is to be steady 

 und prompt. Now, to my somewhat fastidious eye, the Males- 

 Watson device is susceptible of improvement in two minor points. 



First, the slower movement is actuated by a micrometer-screw 

 placed in the middle of the horizontal arm, and the quicker or 

 rougher adjustment has its screw placed at the posterior end of 

 the arm immediately over the limb, i.e. the position of greatest 

 steadiness. 



Now it seems reasonable that if the positions of these were 

 reversed, and the coarser movement were placed at the weaker 

 point, and the more delicate movement at the steadiest point of 

 the arm, an undoubted improvement would be effected. 



Again, the difference between the speeds in the two-speed gear 

 fitted to the Microscope exhibited before this Society was not sufft- 



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