26 
Transactions of the Society . 
III . — A Portable Microscope by J. Zentmayer of Philadelphia. 
By Edward M. Nelson, F.R.M.S. 
(Read 21 st November , 1894.) 
This instrument, while probably the smallest portable Microscope in 
existence, is nevertheless a thoroughly useful one for real practical 
work. It is not, therefore, what so many of these pocket Microscopes 
actually are, a toy. The box in which it is packed is unusually 
small, measuring 4f x 3f X If in. 
A glance at fig. 4 will show that a very early feature is retained 
by making the box the stand (J. Marshall’s Microscope was mounted 
in this manner, 1704). 
This Microscope has a firm and well-made coarse-adjustment. 
The stage, 2f x If in., is plain, having a wheel of diaphragms let into 
its thickness ; it now has a 
sliding bar, but originally it 
was fitted with spring clips, of 
the Powell type, fixed below 
the stage. One word about 
this sliding bar before pass- 
ing on. Mr. Rousselet, the 
owner of the instrument, with 
his usual ingenuity, has fitted 
whalebone instead of steel 
springs below the lugs of the 
sliding bar. This is quite a 
novel feature in microscopical 
construction, and a smoother 
sliding bar I have never used. 
This is a poiut Microscope 
makers might adopt with ad- 
vantage ; a steel spring always 
works stiffly on a brass plate ; 
if the spring is made of metal 
it ought to be brass also, but 
whalebone is better. 
The body, which is 2f in. 
long, is tapped with the Society’s 
screw, it has a draw- tube, which permits of a total extension of in. ; it 
has one Huyghenian eye-piece, and by drawing this out another inch 
of tube-length can be obtained. The illuminating apparatus consists 
only of a concave mirror. The manner in which the stage is mounted 
