the most convenient form of Finder. 
97 
arrow-head, in order to avoid the error that would be occa- 
sioned if the glass were not cut of the ewad dimensions, and 
the wrong end were used in the adjustment. These lines 
should be ruled with a diamond point, filled with plumbago, 
and covered with thin glass. 
It now remains to explain the application of this funda- 
mental starting point for rendering all forms of finders 
universal. 
First, with respect to microscopes without stage move- 
ments. Fig. 1 a, a, is a carrier, made either of metal or 
wood, whose outside dimensions are three and a quarter 
inches long by one and a half wide. Along the lower margin 
is fixed a raised edge, one quarter of an inch broad, for the 
slide to rest against. There is a hole one inch in diameter 
in the carrier, the distance of whose centre is one and a half 
inch from the right-hand end. 
On the left-hand end is fastened to the raised edge, or 
slip, a piece of brass, c, one and a quarter inch square, 
having a sufficient space beneath it to allow the thickest slide 
to pass under, and abut against a stop at the end ; by this 
means an inconvenient length of the carrier is avoided. The 
upper plane surface of this plate contains the index, which 
may be printed on enamelled paper, and contains one square 
inch, divided by lines at distances of one fiftieth of an inch, 
crossing each other at right angles. The two lines which 
cross the centre each way are considerably thicker than the 
rest, and are numbered 25 (being half the number of the 
divisions) ; and the intersection of these is always the start- 
ing point for making the adjustments. Every fifth line from 
this is rather less in thickness, and is numbered at the side ; 
the intermediate ones being as fine as may be convenient for 
