The centre of gravity is that part of a body, round which all its parts are so equally balanced, that, if it be supported, the whole body will be so too.

Take a book, and find, by trial, under what part the finger must be placed to keep the book from falling; that point is the centre of gravity.

Take a rod, or stick, and find that place about the middle of it, under which the finger being placed, it will be balanced; that is the centre of gravity. The moment the centre or gravity ceases to be supported, the whole body falls.

Move a piece of board to the edge of a table, and gradually farther and farther off it; the instant the centre of gravity gets bevond the edge of the table, the board falls.

Run the point of a knife much slanting into the same board, it may then be brought much farther over the edge of the table than it could before, as the knife, leaning the way of the table, brings the centre of gravity that way.

Take a bottle, with a cork in it; stick in the middle of the cork a needle, with the point upwards; then take another cork, and with a knife make a slit in one of its ends, in which place a shilling so far as to make it fast; then take two forks, or penknives, and stick one on each side the cork, slanting a little downwards; then place the edge of the shilling on the point of the needle, and it will rest secure. It may be made to revolve, with great rapidity, on the point of the needle, without falling off.