Procure a small hollow glass vessel, the shape of a balloon, the lower part of which is open, and place it in water, with the mouth downwards, so that the air within prevents the water filling it. Then fill a deep glass jar nearly to the top with water, and place the balloon to float on its surface; tie over the jar with a bladder, so as to confine the air between it and the surface of the water. Press the hand on the bladder, when more water will enter the balloon, and it will soon sink to the bottom of the jar; but, on removing your hand, the balloon will again ascend slowly to the surface. HEATED AIR BALLOON. Make a balloon, by pasting together gores of bank post paper; paste the lower ends round a slender hoop, from which proceed several wires, terminating in a kind of basket, sufficiently strong to support a sponge dipped in spirit of wine. When the spirit is set on fire, its combustion will produce a much greater degree of heat than any ordinary flame: and by thus rarefying the air within the balloon, will enable it to rise with great rapidity, to a considerable height. THE PNEUMATIC TINDER-BOX. Provide a small stout brass tube, about six inches long, and half an inch in diameter, closed at one end, and fitted with a hollow air-tight piston, containing in its cavity a scrap of amadou, or German tinder. Suddenly drive the piston into the tube by a strong jerk of the hands; and the compression of the air in the tube will give out so much heat as to light the tinder; and upon quickly drawing out the piston, the glowing tinder will kindle a match. THE BACCHUS EXPERIMENT. This experiment, showing the elasticity of air, is performed with a pleasing toy. It represents a figure of Bacchus sitting across a cask, in which are two separate compartments. Put into one of them a portion of wine or coloured liquid, and place the apparatus under the exhausted receiver of an air-pump, when the elastic force of the confined air will cause the liquid to ascend a transparent glass tube, (fitted on purpose,) into the mouth of the Bacchanalian figure. To render the experiment more striking, a bladder, with a small quantity of air therein, is fastened around the figure, and covered with a loose silken robe, when the air in the bladder will expand, and produce an apparent increase in the bulk of the figure, as if occasioned by the excess of liquor drunk. THE MYSTERIOUS CIRCLES. Cut from a card two discs or circular pieces, about two inches in diameter; in the centre of one of them make a hole, into which put the tube of a common quill, one end being even with the surface of the card. Make the other piece of card a little convex, and lay its centre over the end of the quill, with the concave side of the card downward; the centre of the upper card being from one-eighth to one-fourth of an inch above the end of the quill. Attempt to blow off the upper card by blowing through the quill, and _it will be found impossible_.