Almost any plane suitable for use in-laboratory work can quickly be prepared for this experiment. The writer uses planes made of 12" pine boards, 3'-6" in length. Two of these boards securely hinged at one end constitute the bed and plane. About three inches from the free end of the plane a screw hook is inserted in the center of the upper surface of the plane. Spring balance No. i is hooked over this hook and onto the car. Spring balance No. 2 is merely hooked into the screw hook. The

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... r then lifts the plane by means of balance No. 2, always pulling at right angles to the plane. Balance No. i evidently gives the component of gravity which is parallel to the plane, while balance No. 2 gives the component which results in pressure against the plane. As a quantitative experiment, or a merely relatively quantitative experiment, the arrangement described is sufficient. If it is desired to make this experiment more quantitative, a screw hook must be inserted in the plane at either side and opposite the center of gravity of the car. The two ends of a cord may then be tied into the screw hooks and balance No. 2 hooked into the loop above the car. The slope of the plane, i. e., the height and length of the plane, may then be taken at the same moment that the reading of each of the balances is taken. These readings may be taken at as many different angles of the plane as may be desired.