.S7A' WILUA.M SIEMENS, F.R.S. 387 



in transmission could be reduced to a small amount. But in 

 1 to the application of the power to cranes or presses there 

 was a loss a loss which might be exceedingly small if the resist- 

 ance to be overcome was nearly equal to the available force multi- 

 plied into the area of the working piston or rain ; but if the load 

 was small, the power expended remained the same as it would 

 be if the maximum resistance was applied, and there was con- 

 sr,|uently great loss. It was interesting to compare that with 

 the case of power transmitted by elastic fluids. In compressing 

 aii- threat power was lost, because the steam in urging the piston 

 forward in the air-compressing pump reduced its volume and 

 raised its temperature, and the rise of temperature occasioned in- 

 creased resistance and loss. The elastic condition of the air was 

 a source of great diminution of power in the first instance, but it 

 was recoverable, inasmuch as the air engine at the other end could 

 be made to work expansively, and thus recover that portion of 

 power which was consumed in compression through loss of volume. 

 But there remained the double loss of heat the heat generated in 

 the compressing pump, which augmented the resistance, and the 

 heat lost in the working of the air engine, which lessened the 

 pressure towards the end of the stroke of the piston. These losses 

 could never be entirely avoided, but they might be reduced, he 

 believed, to 50 per cent., by injecting spray into the compressing 

 cylinder, so as to keep the temperature in compression and in 

 expansion as uniform as possible. Professor Rankine gave the 

 loss as 62 or 64 per cent., but that was under the condition of 

 injecting no water, of compressing air and generating heat in its 

 compression. There was no reason why the air engine should not 

 be made to work as economically as steam. The air did not con- 

 dense, but there was a loss of steam by condensation in the cylinder 

 and in the pipes leading towards it. By injecting warm water 

 into the cylinder the loss of refrigeration might also be avoided ; 

 but that had never been done practically. In transmission air 

 certainly would be less economical than water, for this reason, 

 that water could be transmitted under a pressure of 1 ton or 

 ton to the square inch, whereas air could scarcely be compressed 

 to such a degree ; therefore it was necessary to deal with larger 

 volumes requiring larger pipes and greater frictional surface. 

 Nevertheless for many purposes air would be a preferable medium, 



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