Farrants, on a Micrometer Object-finder. 
93 
movements^ the slide is then to be removed^ and the ruled 
slip put in the same position^ that is^ with its end abutting 
against the lateral stop^ or exactly even with the side of the 
object-plate, as the case may be; the vertical line coinciding 
with the vertical diameter of the field of view will then cor- 
respond with a vertical line on which the object is situate; 
suppose this line is the 40th (from the right of the series, as 
seen in the microscope), the number 40 will then express the 
longitude, and will denote its distance from the left end of 
the slide. It is scarcely necessary to remark, that the slide, 
as well as the ruled slip, must always be placed on the stage 
in the same way, that is, with the same edge always upper- 
most : to ensure this it is well to adhere constantly to some 
plan ; for instance, the rule may be always to keep the label 
on the slide to the right hand. 
If the longitude has been registered as well as the latitude, 
the object will be found by proceeding as follows : — First find 
the latitude by bringing the horizontal line on the ruled slip 
denoted by the number into the centre of the field ; then, 
taking care that the end of the slip is close up to the lateral 
stop, or even with the edge of the object-plate, bring into 
the centre of the field the vertical line denoted by the 
register ; the ruled slip may then be removed from the stage, 
and the slide with the object being put in its place, the object 
will be in the field; and if the observations and manipu- 
lation have been made with correctness, wiU be at or near the 
centre. 
If the eye-piece have an indicator it will be convenient to 
bring it into the field, and to move the object to its point ; 
the line on the ruled slip which corresponds with it may then 
be ascertained with the greatest exactness. If there be not 
an indicator, still, as the eye-glasses will seldom be so clear 
as not to have some mark or speck of dust, any such acci- 
dental mark that may be observed may be made to serve the 
same purpose as the point of the indicator. 
An object once found need never be lost till its position 
has been determined and registered ; for without moving the 
stage or object-plate, the slide with the object may be taken 
off* the stage, and the ruled slip be put in its place : this may 
be moved upwards by the hands while the horizontal lines 
are being counted, and to one side (the right) to enable the 
observer to count the vertical ones ; these being duly noted 
the ruled slip may be taken away, and the glass with the 
object be again put on the stage. If no movement of the 
stage have been made the object should be seen in the same 
