18 EXPERIMENTS IN AERODYNAMICS. 



general of a succession of settings of the wind j^lane beginning with a setting at 

 90° and followed by diminishing angles of elevation. At each setting two obser- 

 vations are usually obtained by turning the register sheet through an angle of 

 180°. Thus the two traces made at the same setting should lie in a straight 

 line passing through the center. 



The method adopted in reading the trfices is as follows : Straight lines are 

 drawn through the center and the two traces made at each setting of the plane. 

 The angle is then measured between the trace of the plane at 90° and the traces 

 corresponding to other settings. The pressure being normal to the 2:)lane, these 

 measured values should be the complement of the angles of elevation at which 

 the plane is set. It will be seen by inspection of the accompanying tables that 

 this relation approximately obtains. 



Tables II, III, and IV contain all the oi'iginal dfita of the experiments and 

 their reduction. The first columns require no explanation. The fifth column 

 (Tables II and III) gives the angle measured on the register-sheet between the 

 radial direction of each trace and the direction of the trace made when the plane 

 was set vertical. The sixth column gives the measured distance of the trace from 

 the center, and the seventh gives the results of these extensions converted into 



pressure on the plane by means of Table I. The column headed ^„, = -=^ contains 



the results of measurements of pressure on the normal plane expressed in terms 

 of the coefficient k,„ of the equation P = k„, V\ in which Fis the velocity of the 

 plane in meters per second and P the pressure on the plane in grammes per square 

 centimeter, the subscript m being used to designate units of the metric system. 



