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VII . — A Simple Form of Mechanical Finger for the Microscope. 
By G. Hanks. 
I wish to call the attention of the San Francisco Society to a device 
for picking up and selecting minute objects under the microscope ; 
in other words, to an improvised mechanical finger, which may be 
easily arranged by any person who possesses a first-class stand. 
Feeling the want of such an apparatus to pick out and arrange 
the interesting and beautiful crystals which occur in the washings 
from the hydraulic gold mines of California, and in the black, gold- 
bearing sands of the sea-coast, I was led to give the subject much 
careful study. 
The elegant mechanical finger described in the ‘ American 
Journal,’ second series, vol. xlix., folio 304, is not only expensive, but 
must be detached from the microscope and laid away when not in 
use, being for this reason inconvenient. Considering these defects, 
I thought on a number of ways to simplify the arrangement, and 
finally hit on a plan to do away with all extra apparatus, and still 
accomplish all that could be desired. The plan is so simple that I 
am almost ashamed to make it public. For aught I know, it may 
be in use by a host of microscopists in different parts of the world, 
but I have never heard it mentioned, nor have I seen it described 
in any of the published works. 
As I am sure that the idea is new to our Society, I will describe 
it as briefly as possible. Let the microscope be placed in a vertical 
position and a suitable object-glass screwed on. Fix the parabola in 
its place in the sub-stage. Let it be pushed as far in as possible, so 
that when elevated by the milled heads, it will rise through the 
opening in the stage, with its upper edge above the surface. As it 
will not be immediately required it may be depressed, using the 
milled heads for that purpose. A glass slide, upon which the rough 
matter is laid, from which it is desired to select an individual crystal 
or other object, may now be placed on the stage. The sliding 
pieces of the stage must then be separated as widely as possible, and 
the stage forceps fixed in the usual position. If the objects to be 
picked out are small, such as diatoms, Ac., a human hair must be 
placed in the jaws of the forceps, and so arranged that it will appear 
in the field and near the surface of the slide. The objects to be 
selected should be as near the centre of the slide as possible. By 
turning the milled heads of the mechanical movements of the stage, 
the desired object may be centred, after which the hair must be 
readjusted without moving the stage. By elevating the sub-stage 
slightly, the slide will be lifted from the stage, the position of which 
can be changed by the mechanical movement, while the slide 
remains stationary. 
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