﻿82 Messrs. H. T. Tizard and D. R. Pye on the 



linked up with the crank pin by the compound connecting 

 rod N. That part of the connecting rod attached to the 

 crank pin is tubular and contains the sliding rod M attached 

 to the hinge L. A clip carried on the sleeve can engage 

 with a collar on the inner rod and hold the latter rigid in 

 the tube. With the connecting rod locked as one link, the 

 crank is rotated by hand for setting the piston in its lowest 

 position. When a compression has to be made, the clutch is 

 suddenly expanded by a hand lever while the flywheel is 

 running at high speed, clutch and crank are carried round 

 with the flywheel, and the toggle joint ELK is straightened 

 until the hinge L lies on the vertical line between the piston 

 centre and hinge K. At the moment when L is vertically 

 over K it comes up against a leather pad, and a clip comes 

 into action which holds it in this position. At the same 

 moment, too, the clip releases the two parts of the com- 

 pound connecting rod, so that while the two rods G and II 

 are held in the vertical position to take the large downward 

 thrust of the piston when explosion of the compressed 

 mixture occurs, the crank, clutch, and flywheel are free to 

 go on rotating, and the shock due to destruction of the 

 momentum of the moving parts is reduced to a minimum. 

 The initial temperature of the gases in the cylinder can be 

 varied by means of a water jacket round the cylinder, and 

 the variation of pressure during and after compression is 

 recorded by means of an optical pressure indicator of the 

 Hopkinson type. 



For the purposes of the present experiments it was 

 necessary : — 



(1) To make the compression space above the piston 



absolutely air-tight so as to eliminate all pressure 

 drop due to leakage. 



(2) To arrange an accurate timing gear upon the 



indicator so that pressure-time records correct to 

 about one per cent, could be obtained. 



(3) To insert some kind of fan in the compression space 



so that the effect of varying turbulence in the 

 compressed gas could be determined. 



(1) Air-tightness of the Compression Space. 



There were three points at which appreciable leakage was 

 liable to take place : — 



(a) Round the sides of the main piston. 



(b) Past the indicator piston. 



(c) Round the fan spindle. 



