87 



Improved Turn-table. By J, Matthews, M.D. 



(Read 27th May, 1870,; 



It may be of interest to members of the Club that I should 

 describe briefly to them my new form of turn-table, or cell machine, 

 by which slides are held and centered, as regards their width, at 

 the same time, leaving their surface entirely free, so that two, 

 three, or more cells may be formed in their length. Everyone who 

 has used the present machine must often have felt the inconvenience 

 of the springs ; sometimes too strong, at others too weak, always 

 in the way, catching the fingers or the pencil, and limiting the 

 number of cells. Centering is also so uncertain that several in- 

 genious remedies have been proposed and used with varying suc- 

 cess; but none have entirely supplanted the old form devised by Mr. 

 Shadbolt, now in use. My plan is simple in the extreme, consisting 

 of two jaws of the average thickness of a glass slide, -| of an inch 

 wide 2\ long. Each of these is pivotted on the face of the turn- 

 table by a screw through its centre, each screw being placed exactly 

 equidistant from the centre of the turn-table, so that the jaws are 

 separated by a space as wide as an average slide; i.e., a full inch. 

 Outside of that space, on one side of the centre of one of the 

 jaws, is a wedge fixed by a screw, in such a way as to be capable 

 of motion in the direction of its length by a slotted hole. This is 

 all the machinery. A B and C D are the two jaws, E is the 

 wedge. On placing a slip between the jaws they probably at 

 first do not touch it. If the wedge be then pushed so as to 

 approximate B to C, the jaws move on their centres, so that 

 however far B may be pushed towards (and moving) C, the 

 other end of C — i.e. D— is moved exactly as much in the opposite 

 direction until they approach near enough to grasp the slide by 

 its edges. The length of the wedge must, of course, be such as 

 to provide for about -|- of an inch variation in the width of slides. 

 It will readily be seen that the slip may be pushed in either direc- 

 tion excentrically lengthwise, so as to allow of the formation of 

 any number of cells, all of which must needs be central as regards 

 their width, if the instrument has been accurately made, which is 

 a very easy matter. I have added also a rest for the hand, F, 

 which may be turned aside on a centre at will, and which I have 

 found to be a great convenience. Its price need very little, if at 

 all, exceed that of the old form. 



