ZOOLOGY AND BOTANY, MICEOSCOPYj ETC. 



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steady means of focusing ; on this point the author says : " In place of 

 the ordinary ring with clamp enclosing the Microscope tube, I apply 

 above and below two segments I V (fig. 102) which accurately fit the tube, 

 most closely however at the edges, so that they are not quite in contact 

 iu the middle. The upper one, next to the eye-piece and micrometer, 



Fig. 102. 



is only fixed to the holder H by a screw so that it can be turned slightly. 

 The other, which is broader at its lower end, has a square pin, which 

 passes through the holder, and is also secured by a screw ; it can be 

 slightly moved sideways by two milled head screws n to bring the reading 

 accurately to 180°. Into the two bearings IV the Microscope-tube 

 T is placed and is held in position by a screw s which passes into the 

 Microscope-tube ; for this purpose a thick ring r, having a screw thread 

 for s, is let into the tube, s is not to be turned so far as to fix the 

 Microscope. Between T and H, and attached to the latter, is a small 

 lever h turning on a screw ; through this s passes and can be slightly 

 raised or lowered by touching the end of the lever after slightly loosen- 

 ing s, which is finally screwed up tight. In this way I obtain a 

 satisfactory fine-adjustment by simple means." 



To clean the micrometer, if necessary, the upper part of the Micro- 

 scope unscrews. The connecting-piece v contains the micrometer m 

 which is to be adjusted parallel to the scale. This would generally be 

 done by rotating the tube in the rings which hold it, but with the above 

 fine-adjustment the tube cannot turn, and it is necessary to elongate v so 

 that it passes down inside T and fits accurately in the lower part of the 



1888. 2 Y 



