26 



ON THE METHOD ADOPTED TO COMl'OUND 



the problem, wlien it occurred to me, Why not turn the old 

 low-pressure cylinder, that was to remain, round on its verti- 

 cal axis, the piston rod, and so bring its steam trunnion 

 amidships, and connect it by a short straight pipe through 

 the condenser between the air pumps to the exhaust trun- 

 nion of the high-presauro cylinder ? 



Now I vontui'o to say that in nine cases out of ttsn, if you 

 tried to do this it would bo found that the columns, frames, 

 and details of the engine would not admit of its being done. 

 However, fortunately for my scheme, T found on trial that 

 the original designer had provided for such a contingency, 

 whether intentionally or not doesn't matter ; suffice it to say 

 that this was practicable in this case. 



The next problem was how to got tho maximum power out 

 of a compound engine having a low-pressure cylinder only 

 66 inches diameter. 



The mean pressure in those cylinders utidor the old condi- 

 tions was 21 1 lbs.; to secure the same result the boiler 

 pressure would have to be about 125 lbs. above that of the 

 atmosphere, a pressure considerably greater than it was 

 prudent to adopt. 



I^ow hero it appeared that I had only got over tho diffi- 

 culty of the steam passages to be wrecked on the rock of 

 steam pressures. 



There was nothing for it but to adopt a more moderate 

 boiler pressure, and consequently a lower indicated horse 

 power and a corresponding redaction in speed. 



For various reasons a boiler pressure of 80 lbs. above the 

 atmosphere was fixed upon, and by putting in a more than 

 usually large new high-pressure cylinder, and carrying tho 

 steam well on through the stroke, tlior'oby get tho greatest 

 possible mean pressure in the low-pressure cylinder. 



Working out this idea, and equalizing tlio jiower in tho 



