mVERTEBKATA, CRYPTOGAMIA, MICROSCOPY, ETC. 617 



tliouglit he would apply clockwork to a table, but on considering the 

 matter, it seemed unnecessary to give it a continuous motion, as a slide 

 can be ringed in a very short time, and the table must then be stopped 

 to remove it. He therefore adopted a method which he considers 

 simpler, more convenient, and less costly. 



The milled portion which is used to spin an ordinary turntable is 

 replaced by a small cog-wheel, and in a horizontal slot in the maho- 

 gany support, in a line with this wheel and gearing into it, is a 

 segment of about one-sixth of a cog-wheel, say 4i inches diameter ; this 

 segment is continually pressed by a strong spring to the left-hand side, 

 against a small indiarubber stop, and has then moved so far as to be 

 out of gear with the small wheel, and plenty of clearance. A trigger 

 in the form of a hook, working vertically in the mahogany — the hook 

 catching the lower side of the segment when pushed over — completes 

 the arrangement. The action is as follows : — The segment is pushed 

 over and is held by the catch, the slide bsing in position. On placing 

 the hand holding the brush on the support, the catch is released, the 

 segment flies round, carrying the table round in the opposite dii-ection ; 

 and clearing it, the table continues to revolve. If we could only 

 manage to remove and replace the slides, a moderately well-balanced 

 and weighty table would turn a sufficient time to ring, perhaps, five or 

 six slides. 



Improved Turntables * — Mr. Eolfe also communicates the fol- 

 lowing (the apparatus having been exhibited at a recent meeting of 

 the Quekett Microscopical Club) : — My object has been to remove the 

 following objections which I have experienced whilst using the ordi- 

 nary turntable. A slide having been partly finished and allowed to 

 dry, it is very difficult to replace it with the cell or ring of varnish 

 perfectly centered, and indeed with great practice such can only be 

 done by a considerable expenditure of time and patience. Again, 

 should a very delicate object be mounted, it is very often driven with 

 the rush of fluid near the outside of the cell, and unless the finishing 

 ring of varnish can be put on correctly it stands great chance of being 

 covered by it. With only the springs to hold the slide it is constantly 

 shifting about, and I have found it most annoying when, as has 

 frequently happened, I have spoilt a carefully mounted object from 

 this cause. 



My first endeavour to avoid these disadvantages is shown in 

 Fig. 1. It consists of a parallel system of levers, actuating two clii>s, 

 working in slots in the table, each clip embracing one corner of the 

 slide. The clips are constantly drawn together by an elastic spring. 

 I found this work admirably for a time, but by wear the slides were 

 not correctly centered, and I found moreover that nearly every slide I 

 used was a trifle out of square, and it was therefore necessary to take 

 care that the same corners were always engaged by the same clips. 

 This fact gave me the idea of a far simpler and equally efficient turn- 

 table, shown in Fig. 2. The top A has two small pins B B pro- 

 jecting about the thickness of a glass slide, and diagonally opposite 



* 'Englisli Mechanic,' xxix. (1879) p. 365. 



