Having made a circular hole in a window-shutter, about three inches
in diameter, place in it a glass lens of about twelve inches focal
distance. To the inside of the hole adapt a tube, having at a small
distance from the lens a slit, capable of receiving one or two very
thin plates of glass, to where the object to be viewed must be affixed
by means of a little gum-water exceedingly transparent. Into this tube
fit another, furnished at its extremity with a lens half-an-inch focal
distance. Place a mirror before the hole of the window-shutter on the
outside, in such a manner as to throw the light of the sun into the
tube, and you will have a solar magic lantern.
The method of employing this arrangement of lenses for microscopic
purposes is as follows:--Having darkened the room, and by means of the
mirror reflected the sun’s rays on the glasses in a direction parallel
to the axis, place some small object between the two movable plates
of glass, or affix it to one of them with very transparent gum-water,
and bring it exactly into the axis of the tube; if the movable tube be
then pushed out or drawn in, till the object be a little beyond the
focus, it will be seen painted very distinctly on a card, or piece of
white paper, held at a proper distance, and will appear to be greatly
magnified. A small insect will appear as a large animal, a hair as big
as a walking-stick, and the almost invisible eels in paste or vinegar
as large as common eels.