TABLE OF CONTENTS With every observation of soaring speed, the horizontal pressure on the plane has been measured by means of a horizontal spring. The detailed observations in Tables XIV and XV contain the number of the spring used, the extension of the spring as measured on the trace in inches, the corresponding pull of the spring, measured in grammes, as taken from the calibration curves, and, lastly, the computed pressure on the plane, obtained by multiplying the pull of the spring by the factor 0.524, which reduces the effect of the actually unequal arms of the instrument to what it would have been were the arms equal. For angles of 90 the instrument affords an additional method of determining the constant of normal pressure, and for all these observations the resulting values of k m and k have been computed. As previously used, the numerical value of k relates to velocities expressed in feet per second and pressure in pounds per square foot, and k m relates to velocities expressed in meters per second and pressures expressed in grammes per square centimeter.
The horizontal pressures on the inclined planes diminish with decreasing angles of elevation, and for angles of 5 and under are less than 100 grammes. Now, for a pressure less than 100 grammes, or even (except in very favorable circumstances) under 200 grammes, the various errors to which the observations are subject become large in comparison with the pressure that is being measured, and...
