To use the apparatus, the paper is to be fixed on the roller, and a strip of lead, or other weight, suspended from the bottom of the paper, to keep it smooth: then, by resting the right hand on the edge of the board B, and turning, with the left hand, the ratchet, the distance of the lines may be regulated by the number of clicks caused by the spring on the ratchet. D, is a foot to support the apparatus, which, however, should be light enough to be held in the hand as a slate.
PORTABLE MICROSCOPE.
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’.
THE PHENAKISTISCOPE, OR STROBOSCOPE.
This amusing instrument consists of a turning wheel, upon which figures are seen to walk, jump, pump water, &c. The disc or wheel should be of stout card-board, upon which should be painted, towards the edge, figures in eight or ten postures. Thus, if it is wished to represent a man bowing, the first position is a man standing upright; in the second, his body has a slight inclination; in the third, still more; and so on, to the sixth position, where the body is most bent: the four following, represent the figure recovering its erect posture, so that the fifth and seventh, the fourth and eighth, the third and ninth, and second and tenth figures, have the same posture. Between each of the figures on the wheel, should be a slit, three-fourths of an inch long, and one-fourth of an inch wide, in a direction parallel with the radii of the wheel, and extending to an equal distance from the centre.
To work this instrument, place the figured side of the wheel before a looking-glass, and cause it to revolve upon its centre; then look through the slits or apertures, and you may observe, in the glass, the figures bowing continually, and with a rapidity proportionate to the rate at which the wheel turns. The illusion depends on the circumstance, that the wheel between each aperture is covered, while the figure goes further. That the deception may be complete, it is necessary that every part of the figures not bowing shall be at an equal distance from the centre of the wheel, and from the slits; also that the figures possess equal thickness and colour.