The science of optics is full of interesting and extraordinary facts which admit of many amuting demonstrations. We need only mention the magic lantern, an instrument that should be possessed by every school; the kaleidoscope, whose changes are not to be counted and by whose means a few bits of broken glass and pearl buttons, in fact any small things having color, may be made to assume the prettiest of shapes, always changing and never twice the same. These and some others are beyond the reach of many, and therefore we illustrate the thaumatrope or wonder-turner, because every child can make one for himself. Cut out a piece of card-board of circular form and affix to it six pieces of string, three on each side. Paint on one side of the card a bird and on the other a cage ; taking care to paint the bird upside-down, or the desired effect will not be produced. When showing- the toy, take hold of the center-strings between the fore-finger and thumb and twirl the card rapidly round, and the bird will appear snugly esconced in its cage. The principle on which this effect is produced is, that the image of any object received on the retina or optic nerve is retained on the mind about eight seconds after the object causing the impression is withdrawn, being the memory of the object; consequently the impression of the painting on one side of the card is not obliterated ere the painting on the other side is brought before the eye. It is easy to understand from this fact how both are seen at once. Many objects will suit the thaumatrope, such as a juggler throwing up two balls on one side, and two balls on the other ; and according to the pairs of strings employed, he will appear to throw up two, three or four balls ; the body and legs of a man on one side, and the arms and head on another ; a horse and his rider; a mouse and trap, but we leave it to the ingenuity of our readers to devise for themselves. Who would ever think that a bottle can be lifted by a straw ? But it can be done in the following manner : take a stout unbroken straw, and bend the thickest end of it, between the knots, into an acute angle, and put it in a bottle so that its bent part may rest against the side of the bottle, as in the above engraving ; then take hold of the eird of it and you will be able to lift up the bottle by the straw, and the nearer the angular part of the latter comes to that which passes out of th neck of the former so much the more easy will be the experiment. In this case, the force being distributed in straight lines, the straw, if it be perfect, cannot break by compression, and there is no tendency to bend it.