EDWARDS, ON FINDERS. 
203 
object to be a Pinnularia grandis, we register it thus, — Pin- 
nularia grandis, together with the number of the slide. 
Fig, 2, 
I have found it very often convenient to write them on the 
back of the indicator itself. 
When the lines on the stage do not exactly correspond to 
one of the lines in the graduations, but fall between them, 
we can, with safety, guess at the distance (thus 25, 5, or 25, 2), 
as I have found that, though in this case the object may not 
always, when it is looked for again, be found exactly in the 
centre of the field of vision, it will generally be within its 
limits. Sometimes, however, the slide may be shifted, so as 
not to lie parallel with the registering lines, and, conse- 
quently they will not cut the same numbered graduations on 
opposite scales ; thus, they may cut 30 in the upper horizontal 
line and 20 in the lower, 10 in the right hand perpendicular 
line and 20 in the left : in this case we register it thus 20x10, 
20 
or else bring it so that they will coincide. In the example 
given it would be 25 in the horizontal and 15 in the perpen^ 
dicular lines. 
It will be noticed, that though there may be faults in the 
graduation of this indicator, it will not make any essential 
diflference in its use, as the indicator is never removed from 
the slide which it registers, and therefore, as I before men- 
tioned, it fulfils the sixth condition of the committee, and 
can be made by the microscopist himself. 
I herewith send a few impressions of this indicator, with 
