If a stick is taken and tapered off to the ends equally from the center, and the stick itself be not too thick, and if it is then placed with its tapered ends resting on two wineglasses, a good smart blow being struck on its center, it will break in two without damaging the wine-glasses. The cause of this involves a curious principle of the laws of force, of which there are many illustrations well known to every one. The blow being given very quickly and evenly, and the substance which strikes having a rapid motion, it is suddenly arrested in its downward course by the stick across the wine-glasses, and it passes through it or breaks it, because there is not time enough for the momentum of the blow to spread along the etick and break the glasses. Another illustration is firing a candle through an inch board. If a gun bo loaded with pow- der, and a candle just fitting the barrel is inserted in place of a bullet, and the gun fired against a door or other piece of wood, the candle will pass through leaving a clean, smooth hole, because when the candle comes to the door, it is evident something must give way, and as the candle is moving so fast, it actually has not time to break, and the wood i's perforated. In many countries of Europe, where liberty has no existence, except in name, letters are opened by the Post-office, an impression of the seal being first taken by striking a piece of lead eharply on it, when the lead receives the impression without breaking the seal. The letter is then opened and read, and re-sealed with the lead reverse, so that the recipient little suspects that his letter has been unfairly opened. The above illustration represents an amusing and instructive experiment, which proves the ascension of heated air by rendering its effects visible, and it may also be used to test the direction of the currents in our rooms and dwellings. To construct one, a piece of card board is taken and cut in the form of a spiral as at A, and to give effect it may be painted to represent a serpent. Then prepare a stand as at B, having a needle in its upper end, and suspend the serpent from its center on the needle, when it will assume the position shown at B. If this be now placed over a Btove, or the tail of the serpent suspended by a bit of thread over a lamp, the heated air ascending through it will cause it to revolve in a very amusing manner. Two serpents may be made to turn in opposite directions, by pulling one out from the one side, and the other in the reverse direction, so that their heads may point towards each other when suspended.