56 LAWRENCE HARGRAVE. 



Plate x. is enlarged from the eighth chronogram drawn by 

 No. 14 engine, and it shows the pressures in the air pipe during 

 one double vibration. The receiver pressure being about 125 lbs. 

 per square inch. The chronogram consists of a series of jumps 

 which cease when the receiver pressure falls to about 483hs. 



The partial interpretation of Plate x. may be stated in this 

 manner, beginning at the left hand side. The vertical scale is 

 pounds per square inch, and the horizontal scale 100th of a second. 

 The reduced pressure reads 47R>s. as the piston reaches the top of 

 the cylinder and the valve springs to the position that admits air 

 to the top of the piston. Before the piston can be moved down 

 at all the inertia of the wings has to be overcome. This takes 

 time, and the diagram shows it took -028 of a second to start the 

 piston, but during this time the air was coming through the 

 reducing valve and charging the passages and clearance together 

 with the pipe leading to the indicator with high pressure air, this 

 pressure rose to 89K)s. per square inch before the wings began to 

 rise, and immediately they did so the pressure fell. 



It will be noticed that there are two smaller jumps in the 

 diagram as the wings are rising : one is made shortly after the 

 wings begin to move, and the other when the pressure has fallen 

 to the point determined by the tension of the reducing valve spring 

 and the wing area. As these irregularities do not occur when the 

 wings are falling it is safe to assume that they are not caused by 

 any stickiness of the pen, indicator piston or reducing valve. 



At *18 of a second from the beginning of the diagram the valve 

 springs to its lower position, the piston remains stationary for 

 •035 of a second, and the pressure rises to 851bs. per square inch 

 before the wings begin to strike downwards ; in *0T of a second 

 the pressure has fallen to that to which the reducing valve was 

 adjusted : *085 of a second elapses before the piston reaches the 

 top of the cylinder and the cycle is complete. The double vibra- 

 tion has occupied *37 of a second, during -063 of a second of which 

 the wings were stationary. The mean pressure during the double 



