7 
“i 
A. S. Johnson on an Indicator Stage for Microscopes. 387 
from its centre to the points 40 and 70 in its horizontal line, the 
right hand index is made to stand at 70 on the right scale and 
the left hand index at 40 on the left scale. When the stage is 
set at 70 and a slide placed on the stage with its right vertical 
in coincidence with the right vertical on the stage, its pusition 
will be the same as if the slide were placed upon the universal 
indicator, with the right vertical at 70 of its horizontal gradua- 
tion. It is hardly necessary to add that a motion of the stage 
carrying the slide is exactly equivalent to a motion in the same 
direction and of the same extent of the slide alone upon the uni- 
vérsal indicator. 
he top plate of the stage is furnished with a slide holder 
moving in grooves, by means of which a slide may be easily 
adjusted so that its horizontal guide line shall coincide with the 
horizontal line on the stage. This adjustment having been made, 
its right or left vertical is to be made to coincide with the corre- 
sponding vertical on the stage. he right verticals are to be 
used for numbers of the horizontal graduation from 60 to 110, 
and the left for those from 0 to 50. 
n case of an object alieady registered, all that remains to be 
done is to move the stage by the milled heads of the pinions till 
the indexes stand at the registered numbers, and the object will 
at once be found. In case of a slide not registered when an ob- 
ject is found which it is desired to record, a glance at the indexes 
will give the proper numbers to be recorded. 
It will be noticed that the vertical graduations extend only 
from 80 to 20. This being equal to 12th inches, affords ample 
room for all ordinary slides not covered with paper. But as 
some slides are still so covered, provision has been made for 
them. On the stage parallel to the horizontal line two others are 
engraved each 2ths of an inch distant from the first. This dis- 
tance being exactly equal to 20 divisions on the scales, in order 
to find an object registered by the universal indicator from the 
front edge of the slide, the same edge must be brought to the 
front line and the stage be set at 20 more than the registered 
bumber. If on the other hand the registration has been made by 
the lower edge, the rear line must be used and the stage set at 20 
ss than the registered number. In registering objects on such 
slides by the indicator stage, the registration ought always to be 
made as the numbers would appear on the universal indicator. 
To effect this it is only necessary, if the front line be used, to 
deduct 20 from the number indicated, if the rear line to add 20. 
he manipulation with this stage is by no means complicated. 
the stage before you, it can be mastered in ten minntes, and 
hen once mastered its convenience and value are great. Regis- 
tered objects can be found and new ones registered with great 
rapidity. To illustrate the great saving of time which it effects, 
