Zoophytes must of course find a place in the cabinet, and the young microscopist ought to put up a few specimens of the “bird’s-head” processes which are found in the bugularia and other inhabitants of the sea. The pretty noctiluca, to which is mostly owing the phosphorescence of the sea, should be preserved, and the extraordinary appendages to the skin of certain star-fish and sea urchins should be examined. These are called pedicillariæ, and a sketch of them is given in the [illustration].
OPTICS AND OPTICAL AMUSEMENTS.
“‘Seeing is believing,’ so the sages say,
To prove this false, hear me, my friends, I pray,
And very soon you all will be agreeing,
That nought is so deceptive as our seeing.”—Martin.
Optics is the science of light and vision. Concerning the nature of light, two theories are at present very ably maintained by their respective advocates. One is termed the Newtonian theory, and the other the Huygenean. The Newtonian theory considers light to consist of inconceivably small bodies emanating from the sun, or any other luminous body. The Huygenean conceives it to consist in the undulations of a highly elastic and subtle fluid, propagated round luminous centres in spherical waves, like those arising in a placid lake when a stone is dropped into the water.
LIGHT AS AN EFFECT.
Light follows the same laws as gravity, and its intensity or degree decreases as the square of the distance from the luminous body increases. Thus, at the distance of two yards from a candle we shall have four times less light than we should have, were it only one yard from it, and so on in the same proportion.
