TABLE OF CONTENTS As preliminary to obtaining the data mentioned at the close of the last chapter, it is desirable to determine experimentally the direction of pressure of the air, (since the air is not an ideal fluid such as the theory contemplates,) on an inclined plane, and to investigate the assumption made by Newton that the pressure on the plane varies as the square of the sine of its inclination.
The second instrument constructed was, then, for the purpose of obtaining graphically, the direction of the total resultant pressure on an inclined plane (in practice a square plane) and roughly measuring its amount. [*] For this reason it will be called here the Resultant Pressure Recorder.
Plate V contains drawings of the instrument. Upon a base-board, BB ?, is a standard, E, carrying an arm, AA ?, hung symmetrically in gimbal joints. On the outer end of the arm a one-foot-square plane (called here the wind plane) is fastened with a clamp, and a graduated circle assists in setting the plane at different angles of inclination to the horizon. The extremity of the inner end of the arm carries a pencil, P, which registers on the surface of a vertical plane, which is in practice a sheet of diagram paper clamped on the surface FF ? of an upright circular board fixed by a standard to the base-board BB ?. The pencil-holder H fits closely into a ring at the center of a system of four...
