If a rectangular plane be made to move through the air at an angle of inclination with the direction of advance, it was implicitly assumed by Newton that the center of pressure would coincide with the center of figure. Such, however, is not the case, the pressure being always greater on the forward portion, and the center of pressure varying with the angle of inclination.

The object of the present chapter is to present the results of experiments made to determine the varying positions of the center of pressure for varying angles of inclination of a plane moved in a horizontal course through the air. Drawings of the apparatus devised for this purpose are given on plate V. AA ? represents the eccentric wind-plane one foot square held in a brass frame about 5/8 of an inch wide and 5/8 of an inch thick. Two sliding pieces, SS ?, move in a groove in the edge of the brass frame, and may be clamped in any position by screws. Each sliding piece has a small central hole, in which fits a pivot. V. The wind-plane (eccentric plane) is suspended by these pivots and swings about the axis passing through them, so that by moving the plane in the sliding pieces this axis of rotation can be moved to any distance up to two inches. A flat lead weight, which also slides along the back of the plane, can be adjusted so as to counterpoise it in any...