THE FINE ADJUSTMENT 173 



at C, raises or lowers the body with great smoothness and with the 

 great delicacy of ^.^th inch for every revolution of the milled head, 

 and therefore capable of yielding good service with the highest power 

 objectives. 



We may now direct our attention to the former of the two divisions 

 into which we have separated the various kinds of fine adjustment, 

 viz. that in which the nose-piece only is controlled by the adjustment 

 screw. 



Swift's vertical side lever is oije~of the new forms of fine adjust- 

 ment worthy of careful trial ; it has in it elements of great merit. 

 It can. however, only be applied to the Lister model, and with the 

 adjustment described above certainly places this form, of microscope 

 beyond the danger that some years ago promised to have proved its 

 extinction as a first-class microscope. 1 



The first form of this adjustment (1881) was sound in principle and 

 ingenious in construction, and although the patentee introduced a 

 modification 2 of it (1885), we believe the original form, which he still 

 makes, to be the best, because it only acts on the nose-piece while the 

 modification acts on the body-tube. 



The early form employed by Swift avoided what had been a sheer 

 necessity of all successful fine adjustments of this type, viz. the 

 accuracy and perfection of the fitting of the nose-piece tube. This 

 was done, as shown in fig. 133, by attaching a vertical prism-shaped 

 bar, A, to the nose-piece, and sliding this in V-grooves in a box 

 at the back of the body. A horizontal micrometer screw with a 

 milled head, F, acts on a vertical bent lever, D, on which a stud, E, 

 fixed to the prism bar bears. 



There is also an adjustment for tightening up the prism bar in 

 the V-grooves, B B. Side-shake and ' loss of time ' are impossible 

 with this form of adjustment ; while the power to ' tighten up ' by 

 means of the capstan-headed screws enables wear and tear to be 

 compensated. It is obvious that the slowness of the motion is here 

 controlled by three factors : (1) the length of the lever, D ; (2) the 

 distance of the lifting-stud, E, from the pivot or fulcrum ; and 

 the pitch of the screw-thread on F. 



Manifestly, where a side-lever fine adjustment such as this is 

 employed it should be, as it now always is, placed on the left-hand 

 side of the operator : we can readily focus with the left hand, and 

 leave the right hand free for moving the slip and effecting other 

 adjustments. Ambi-dexterity is not at present a common gift, and 

 to have the right hand free is important. This was pointed out by 

 Mr. Nelson when this fine adjustment was first introduced, and he 

 had a student's microscope constructed with the micrometer milled 

 nead on the left side, as in fig. 134. It is manifest, however, that 

 it w T ould greatly improve this adjustment if the screw-pinion 

 were carried right through and a milled head placed on both the 

 right and the left sides of the body. 



An early form of a nose-piece-controlled Jine adjustment was em- 

 ployed by Andrew Ross. It was applied to a microscope having a 



1 Journ. B.M.S. (1881) p. 297, fig. 43. 



2 Journ. E.M.S. (1885) p. 120 and (1886) p. 1043, fig. 207. 



