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nydus/How it WorksPublic

Archibald Williams explains the scientific principles behind common mechanisms and physical phenomena such as steam, electricity, light, and hydraulics. The text focuses on the fundamental operation of everyday devices rather than specific models or detailed technical specifications.

Page 182 of 446
Table of Contents

HOW IT WORKS.

a convex lens; when thinner, a concave lens. The names of the various shapes are as follows:—No. 1, plano-convex; No. 2, plano-concave; No. 3, double convex; No. 4, double concave; No. 5, meniscus; No. 6, concavo-convex. The thick-centre lenses, as we may term them (Nos. 1, 3, 5), concentrate a pencil of rays passing through them; while the thin-centre lenses (Nos. 2, 4, 6) scatter the rays (see Fig. 105).

Fig. 104.
Fig. 104. —Six forms of lenses.

THE CAMERA.

Fig. 105.
Fig. 105.
Fig. 106.
Fig. 106.

We said above that light is propagated in straight lines. To prove this is easy. Get a piece of cardboard and prick a hole in it. Set this up some distance away from a candle flame, and hold behind it a piece of tissue paper. You will at once perceive a faint, upside-down image of the flame on the tissue. Why is this? Turn for a moment to Fig. 106, which shows a "pinhole"

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