650 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
single foot back, wide open in front. The pillar may be single or 
double, but must have thumbscrew at the joint to hold it firm at any 
desired inclination ; the mirror on swinging arm, adapted to carry a 
condenser if desired, and the stage just high enough to admit a short 
Abbe condenser; the centre of rotation of the mirror-bar just above the 
stage. The arm is a box-arm, Jackson model, shown with one side 
removed. The barrel should 
be of the short type and is 
supported on an X-shaped 
bar, that slides between the 
Y’s on each inside of the 
box-arm, as shown by de- 
tailed section. A steel tape 
or picture cord is fastened 
at each end of the X-bar, 
one end being the tighten- 
ing screw F. This tape is 
wound once round the 
grooved wheel A, which is 
turned by the usual milled 
head and gives the coarse- 
adjustment to the instru- 
ment. On each side of the 
wheel A and on the same 
axis are two discs B B. 
that pinch the wheel A 
between them by a screw 
and act as a friction clutch. 
These discs are prolonged 
downward in the curved 
bar against which presses 
the spring E. The micro- 
meter screw D forces the 
bar against this spring, 
and, turning the wheel A 
by friction, forms the fine- 
adjustment. Every part of 
the instrument is adjustable 
for wear. The stage is a 
ring, with a plate of glass 
dropped in it. A Zentmayer 
sliding holder may be used. 
The c mdenser is not shown 
in detail, as no special features are claimed for it. I am aware that 
friction fittings are not new; one was described by Mr. Wenham, vol. 
vii., Q. J. M. ; also a chain movement was made by Pike or Grunow, 
of New York city, about 1850. Nevertheless, these devices do not 
appear to me to be as useful as that here described. The steel tape 
has proved successful in mechanical combinations where racks, &c., have 
failed, and it may succeed in the Microscope. The micrometer screw D 
may be replaced by a cam. 
