248 



On some Improvements in Microscopical Turn-Tables. 



By C. Spencer Rolfe, C.E. 



Plate. XIV. 



{Read May 23rd, 1879.) 



About a year or more since, after having my patience somewhat 

 exceptionally tried in using an ordinary Shadbolt's turn-table, I de- 

 termined to try and devise some better means of securing the sMe 

 than the ordinary springs, and permitting it to be removed and re- 

 placed without trouble. The result of my efforts I purpose now 

 detailing, in the hope that they may be useful to fellow-mounters of 

 microscojDic objects. 



Discarding the means usually adopted for centering work in the 

 lathe, as being too complex and difficult of construction for my pur- 

 pose, I devised the arrangement shown in Fig. I. Two opposite 

 portions of the top are cut away, forming guides, in which the two 

 V-shaped clips slide. These being moved equally from and towards 

 the centre, by a system of levers, (shown dotted, and working on the 

 underside of the turn-table,) which are constantly kept in such a 

 position by an elastic spring, that the clips approach one another. 



On the longer of the levers are two knobs, and by pressing either 

 of them round with the finger, the clips open, and a slide being placed 

 between them, and the finger removed, they spring together and 

 firmly hold it, in such a position, that, had the movement been 

 so constructed, the centre would be exactly over the centre of 

 the table. In practice it has been found preferable to have the slide 

 just a trifle out of centre, and by this means it is always possible to 

 replace a ringed slide with the same corners embraced by the same 

 clips, and if this is not done it is at once rendered visible. Were 

 every slide made truly square, this would be unnecessary. A turn- 

 table constructed on this principle was shown to some of the mem- 

 bers at the last annual general meeting, and I was then informed by 

 our Hon. Secretary that one for the same purpose had been described 



