CORRESPONDENCE. 
133 
A A are right-angled clutclies or clamps, set loosely upon the lugs B B 
by screws, allowing free rotatory movement upon the screws, so that 
the clutches may conform easily, and without assistance, to various 
sizes and forms of slides. The lugs B B are fitted to and move in the 
slots E E, and are carried upon the right and left screw C C, which is 
turned by the milled head D, thus approximating or separating the 
clutches A A, simultaneously and at the same rate, towards or from 
the exact centre of the table. 
The rest of the apparatus is like the ordinary turn-table, except 
perhaps as to size. Upon the scale to which these figures are drawn, 
the table, which is 4 inches in diameter, will take any slide froni 
about 3^ by 1^ inches, down to about 2 inches square. 
It will be readily seen that the point of revolution of the slide 
must be the place where its two diagonals cross, no matter what its 
size or shape may be. If the slide is perfectly rectangular, this point 
will, of course, be the exact centre as to both width and length. If 
the angles vary a little from right angles, this point will be very 
nearly the centre, — practically nearly enough. 
This form of table, therefore, not only secures uniformity in the 
original placing of cells and objects upon slides, but also ensures 
perfect concentricity in finishing. It is almost always necessary to 
apply several different kinds or coats of cement or varnish upon the 
same slide, and every preparer of objects knows what uncertainty 
there is of centering a slide a number of times alike upon the turn- 
table now in common use. By this arrangement, however, there can 
be no difficulty in always replacing a slide upon the table in precisely 
the same position. 
If this contrivance should meet with general favour, and be adopted 
by all preparers of microscopic specimens, it would become, to objects, 
what " the London Society's screw " is to objectives, — a universal 
standard. For if Moller and Wheeler, and other mounters, use this 
table, anyone else who has one can always centre their slides just as 
