54 



EXPERIMENTS IN AERODYNAMICS. 



The extensions of the spring corresponding to the horizontal component of pressure 

 on the plane, and caused by the movement of the Recorder about the A^ertical 

 axis, are taken from the sheet of the recordino- cylinder carried on the turn-table 

 arm, as ah'eady described and as shown on jilate 7. The records of velocities 

 are found on the stationary chronograph registering the quadrant contacts of 

 the turn-table, and on the same sheet with the electric contacts made at soaring 

 speeds. Thus, when the latter sheet has been taken off its chronograph barrel, 

 the observer has before him a permanent record of the velocity of the turn-table 

 measured four times in every revolution, and together with it the trace of the 

 irregular contacts made by the vertical rocking of the balance arm which takes 

 place at soaring speed. Now, since the criterion of exact soaring is that these 

 signals shall appear on the trace half the time of each revolution, an inequality 

 mark is added to the record of the measured velocities, which indicates how 

 nearly this condition is attained. If the chronograph sheet for any complete 

 revolution of the turn-table is more than half filled with the signals, the velocity 



