° 
J. W. Bailey on a Universal Indicator for Microscopes. 59 
Should it ever be desired to reproduce the Indicator by engra- 
ving or otherwise, the dimensions above given must. be most ac- 
curately preserved. The dimensions her@ given were taken from 
the standard inch of the United States @elonging to the State of 
Yew York and preserved in the office of the Superintendent of 
Weights and Measures in Albany. It is the same as the English 
inch. 
The slides on which objects are mounted to be used with the 
Indicator must have guide-lines ruled on their under side as 
shown in fig. 1 and 2. The horizontal line parallel to the lower — — 
edge and passing through the middle of the slide is not continued — 
over the portion of the slide which is to be occupied by the objects” 
and their glass cover. The distance of each of the vertical lines 
from the middle point of the slide is one inch. Great accuracy 
in the distance between these lines of the slide is not essential 
when they are to be used with the ordinary form of the Indica- 
tor as above given, but it is desirable when they are to be em- 
ployed as hereafter described with a modification of the Indicator 
applied to a moveable stage ge 
The slides should all be marked with an arrow placed upon 
their upper and right hand corner, as shown in fig. 1 and 2, to 
point out the edge which must always be kept in front in using 
the slides upon the Indicator. 
_ The Indicator is to be used as follows:—Cut ont the. centre 
a thin bladed knife following the outline G, H, 1; then 
piece with 
Teplace the piece cut out, and make a hinge for it along the lin 
either b ; t ler so that when any object 
vy the fingers or a moveable ruler I oad aa ok the 
Microsc : in n the slides shall pass 
ope, the horizontal guide line upo Pa tsdicaior as 
temote from each other as possible. In some positions of the 
slide the axes A, and B’ can be used for this purpose; 1n others 
A, and A’, or B, and B’ must be employed. ; 
The horizontal line of the slide being arranged as just directed 
it will be found that at least one of the vertical guide lines of the 
