[Illustration]
This cheap and useful instrument consists of a handle of hard wood,
_a_, which is screwed into a brass piece, _d_, having, at its top, a
ring, with screws on back and front, into which are to be screwed two
cells with lenses of different foci. There is also a projecting piece
formed on the side of the brass piece, _d_, in which is a hole to
receive the screwed end of a cylindrical rod of brass, _c_. Upon this
rod, a springing slit socket, _e_, slides backwards and forwards, and
is also capable of being turned round. This socket has affixed to it,
on one side, a projecting part, with a screwed cavity in it, to receive
a short screwed tube, with a small hole in its centre, made to fit the
steel stem of the spring forceps; a corresponding hole being made at
the bottom of the screwed cavity, where is lodged a piece of perforated
cork; which, being pressed upon by the action of the screw, closes upon
the steel stem of the forceps, and steadies them, and the objects held
in them. The stem of the forceps being removed from its place in the
short tube; the handles and lenses, and the rod, _c_, and the sliding
socket upon it, being unscrewed from its place in the handle; they can
all three be packed in a black paper case, which is only three and a
half inches long, one inch broad, and half an inch thick.
This microscope possesses three different magnifying powers, namely,
those of two lenses separately, and the two in combination.
Microscopes of a still simpler nature are small globules of glass,
formed by smelting the ends of fine threads of glass in the flame of a
candle; and small globular microscopes of great magnifying power, made
of hollow glass about the size of a small walnut, may be purchased very
cheaply at the opticians’.