the most convenient form of Finder. 
99 
In registering a large cabinet of Diatomacece, Desmidiem, 
%cc., it will only be necessary to number tlie slides^ and to 
enter on a printed list of these objects^ the number_, latitude, 
and longitude where they may be found. By these means 
any specimen may be placed under the microscope in less 
than a minute. 
The finder may be applied to microscopes having stage- 
movements by merely laying the carrier against the horizontal 
straight edge on the top plate ; and_, after fixing the rotary 
plate (if there be one) by a pin passed into a hole drilled 
through this plate and the next, the adjustments already 
described may be made, using the milled heads for the pur- 
pose. In those microscopes which have the longitudinal and 
perpendicular sliding plates divided into fiftieths of an inch, 
the principle of a universal finder may be applied in a very 
simple manner. The rotary movement being fixed in the 
above mode, there must be a stop, consisting of a strip of 
plate brass, with one end turned up, to form an abutment, 
and the other slotted and passing under the head of a screw 
in the top plate, so as to move with sufficient friction to 
retain its position. 
The graduated scales should then both be set to read 25, 
and the standard placed on the stage. Then bring the cross 
into the centre of the field by shifting the stop laterally, and 
moving the top plate, or straight edge, perpendicularly, taking 
care to keep the standard hard against both its bearings. 
When this has been effected the standard may be removed, 
and, if any slide be placed in the same position against the 
stop and ledge, the objects in it may be registered and found 
by means of. the graduated scales, freely using the stage- 
movements for the purpose, but being carefal not to shift 
the top plate or sliding stop. 
This form of finder is to be recommended where rectilinear 
stage-movements exist, on account of its simplicity. A sub- 
stitute for the graduated scales may be obtained by cutting 
ofi" the edges from two of the square index-plates here 
described, and cementing them in the most convenient situa- 
tions. 
Another method would be to fasten one of the entire square 
scales on the top plate of the microscope ; but this would 
involve the necessity of a pointer, as in the case of using the 
carrier. 
Having now described a finder that can be used either 
with the most simple form of microscope, as a temporary 
addition to the ordinary stage-movements, or as permanently 
incorporated with them, we by no means desire arbitrarily 
VOL. V. i 
