The largest drinking-glass holds but half a pint, so that your diving light soon goes out for the want of air. As an average, a burning candle consumes as much air as a man, and he requires nearly a gallon of air every minute, so that, according to the size of the glass over the flame, you can calculate how many seconds it will remain alight; of course, a large flame requires more air than a small one. For this, and several other experiments, a quart bell-glass is very useful, but being expensive it is not found in every parlor laboratory: one is, however, easily made from a green glass pickle-bottle; get a glazier to cut off the bottom, and you have a bell-glass that Chilton would not reject. To Place Water in a Drinking-Glass Upside Down. Procure a plate, a tumbler, and a small piece of tissue or silver paper. Set the plate on a table, and pour water in it up to the first rim. Now slightly crumple up the paper, and place it in the glass; then set it on fire. When it is burnt out, or rather just as the last flame disappears, turn the glass quickly upside down into the water. Astonishing! the water rushes with great violence into the glass! Now you are satisfied that water can be placed in a drinking-glass upside down. Hold the glass firm, and the plate also. You can now reverse the position of the plate and glass, and thus convince the most skeptical of the truth of your pneumatic experiment. Instead of burning paper, a little brandy or spirits of wine can be ignited in the glass; the result of its combustion being invisible, the experiment is cleaner. AMUSEMENTS IN MECHANICS. There is no subject so important as mechanics, as its principles are founded upon the properties of matter and the laws of motion; and, knowing something of these, the tyro will lay the foundation of all substantial knowledge. The properties of matter are the following: Solidity (or impenetrability), divisibility, mobility, elasticity, brittleness, malleability, ductility and tenacity. The laws of motion are as follows: 1. Every body continues in a state of rest, or uniform rectilineal motion, unless affected by some extraneous force. 2. The change of motion is always proportionate to the impelling force. 3. Action and reaction are always equal and contrary. Experiment of the Law of Motion. In shooting at “taw,” if the marble be struck “plump,” as it is called, it moves forward exactly in the same line of direction; but if struck sideways, it will move in an oblique direction, and its course will be in a line situated between the direction of its former motion and that of the force impressed. It is called the resolution of forces. Balancing. The center of gravity in a body is that part about which all the other parts equally balance each other. In balancing a stick upon the finger, or upon the chin, it is necessary only to keep the chin or finger exactly under the point which is called the center of gravity. The Balanced Coin.