( 1 60 ) Monthly Microscopical 
Journal, Sept. 1, 1870. 
PROGRESS OF MICROSCOPICAL SCIENCE. 
A New Mechanical Finger for the Microscope.—Mr. J. Zentmayer 
gives the following description of a recent invention by him in the 
‘Journal of the Franklin Institute’ for May:—In the study of 
diatoms it has been long desired to find a substitute for the clumsy 
fingers of the human hand to do the delicate work of picking up rare 
and valuable diatoms detected by the microscope, and to transfer them 
to a glass slide for preservation. Prof. H. L. Smith, well known by 
microscopists as the inventor of several valuable accessories to the 
microscope, first presented us with a very ingenious little instrument 
of that kind. Messrs. John H. B. Latrobe and George Dobbin, of 
Baltimore, two expert microscopists, had in use for some time one 
of these instruments, but found it difficult to work it; and as the 
instrument was exceedingly well made, this proved that its construc- 
tion was too complicated to give the firmness required in picking up 
a shell less than the thousandth part of an inch in length, and of 
which a single ounce of ocean sand contains, sometimes, many millions. 
Mr. Latrobe invited me to design and construct for him an instru- 
ment for this purpose. The instrument requires many adjustable 
movements, and each of these increases its liability to shake and 
spring. So I made it my object to utilize such movements of a first- 
class microscope stand as are not essential for other specific opera- 
tions, as parts of the new finger. I found in the movements of a 
mechanical or sliding stage the main movements required in the 
finger, and so attached the apparatus to the mechanical stage. This 
gave me two of the most important movements, with a firmness and 
with dimensions of parts for which, otherwise, there would be no 
room. This step, however, made it necessary to provide for another 
stage; but as there is never a higher power than a 2rds employed with 
such an apparatus, a plain stage with some simple arrangement to 
hold the slides would be 
found quite sufficient — 
such a one was therefore 
arranged. The cut repre- 
sents the finger attached 
to one of my large micro- 
scopes. <A is the top plate 
of the mechanical stage ; 
the circular plate is omitted. 
The cap B is fitted to the 
lower body below the stage, 
into which cap the new 
sub-stage C is fastened by 
a narrow tube, wide enough 
to admit illumination from 
the mirror. As the lower 
body is movable up and down by a rack, another movement is 
gained which is necessary to accomplish our result. The difference 
nT] 
TTA 
