90 



EXPERIMENTS IN AERODYNAMICS. 



pressure is at the axis of rotation. The measurement of this angle is, therefore, 

 the object of observation. 



In actual experiment the exact angle of equilibrium of the plane is masked 

 by slight inequalities of speed and by fluctuation of the wind, and there is oscil- 

 lation aboul a mean position. In measuring the trace, the extreme angles of this 

 oscillation were read, as well a.s the mean position of equilibrium. 



The following transcript from the note-book for September 22. 1888, will 

 afford an illustration of the detailed records made in connection with each series 

 of experiments. The column headed ''range" gives the range of oscillation of 

 the plane, and shows that the plane is far more unsteady when the axis of oscil- 

 lation and center of pressure is very eccentric than when it is nearer the center. 



September 22. ISSS. 



Meteorological conditions not so favorable as yesterday, the wind being rather strong. 



Engine run by Eisler; J. Lude\Yig sets wind-plane; F. W. Very attends to chronograph and records. 



Two complete sets of observations were made, both on September 1*1 and 

 September 22, 1888, making in all 31 separate readings, which are given in detail 

 at the close of the chapter. 



The mean of these observations is presented in the following table XVII : 



