A New Form of Fine Adjustment. By E. B. Stringer. 421 



the Microscope is set horizontally this screw is run out to its full limit, 

 leaving just sufficient tension in the spring to work the movement 

 in this position. Also should a binocular body or unusually heavy 

 nose-piece be in use in ordinary work, the tension of the spring may 

 with advantage be increased in proportion, by slightly screwing it up. 



It would seem that only by such means can a high degree of 

 sensitiveness be maintained under all conditions, in movements which 

 actuate the entire body. 



Another point of importance is that the body, as will be seen, is 

 drawn downwards by the lever, and drawn upwards by the spring ; 

 the force in each case being applied exactly in the line of motion ; so 

 that, even should the pillar fit loosely and side shake be possible, it 

 does not for the most part occur. Arrangements (and there are 

 several) in which the body is pushed against an opposing spring, 

 tend much to increase the liability to every kind of side shake and 

 jamming. 



Also, seeing that the moving part is firmly held between the lever 

 below and the spring above, any alteration of focus when the milled 

 head is at rest is quite impossible; a point of great importance in 

 photomicrography. 



The movement is well protected from dust, and is of sufficient 

 strength to withstand the roughest treatment. It may be taken 

 apart with great ease, it being only necessary to unscrew the trans- 

 verse steel pin, and remove it and the roller, when the whole may at 

 once be lifted off the pillar. 



I should add that Mr. Nelson, who saw my drawings before 

 Messrs. Watson made the instrument, suggested that the pillar 

 should be slightly hollowed out at the sides, so as to bear only at its 

 edges, thus guarding against the possibility of any lateral rocking 

 movement. He subsequently suggested that the back plate should 

 be slightly sprung by cutting away the underlying metal in four 

 places ; also that the pillar should be made wider and considerably 

 truncated in front, so as to form a bar similar to that in the coarse 

 adjustment of Powell's large stand. All these three improvements 

 have been carried out in the present instrument. 



Careful trials since made have shown that with this form of pillar 

 the strongest spring works perfectly well, without the least tendency 

 to the production of side shake, either in the vertical, inclined, or hori- 

 zontal position. The adjustment controlling the tension of the spring, 

 therefore, loses much of its importance. Very critical workers might 

 still, however, find it advantageous. 



