98 
Report of Committee for ascertaining 
distinct observation. The exact position in which the paper 
index is pasted on is not of material consequence^ provided 
it lies square with the carrier. 
The method of using this finder is as follows : — First take 
the standard y and place its marked end against the abutment 
under the index-plate of the carrier^ and see that it rests 
upon the bottom ledge. Then place them both together 
under the microscope_, with an object-glass attached. By 
sliding up or down the vertical moving straight edge (with 
which every plain stage should be fitted), and by shifting the 
carrier sideways against this edge, bring the cross into the 
centre of the field. A moveable index, or hand, is now made 
to point to the centre, or crossing of the thick lines on the 
index-plate, and there fixed fast. This hand, or pointer, is 
simply a thin, flat piece of brass, turned round like a hook 
or staple, having the longest limb ending in a point, and the 
shortest slotted, to be clamped to the under side of the fixed 
stage-plate, by means of a milled-headed screw passing 
through the slot. 
The longitudinal adjustment of the pointer is performed 
by thrusting it endways, and the transverse by turning it 
- sideways. Now look through the microscope again, to ascer- 
tain if the cross on the standard is still in the centre of the 
field, and coincident with the adjustment of the pointer. If 
so, remove the standard, and replace it by the slide contain- 
ing objects whose position is either to be registered or found. 
If the pointer is not in the way when not in use, it may re- 
main fixed j and readjustment by the standard will be un- 
necessary except for occasional verification. It is now 
evident that the centre of the field is represented by 
the pointer on the index-plate at an invariable distance; 
therefore, if the carrier be always moved in straight lines at 
right angles, the pointer will indicate the latitude and longi- 
tude of the object under the microscope at the time. 
Although the centre of the slide is taken as the most con- 
venient point for adjusting the index, it is best to consider 
the lower horizontal line on the index-plate as the equator, 
and the left-hand perpendicular one as the first meridian ; by 
which means all the latitudes will be north, and the longi- 
tudes east ; and, if the first figure be invariably appropriated 
to the latitude, the registration will be very simple. Should 
it be necessary to register smaller quantities than the fiftieth 
of an inch, the amount may be estimated with sufficient 
accuracy, and added as a decimal figure ; and this will be 
found much easier in practice than the reading of very fine 
divisions. 
