TOO TRANSACTIONS OF THE 



of the steam to its purpose in the engine itself, on the following 

 grounds : Steam finds less resistance to its action in this engine, 

 for, on account of the great pressure, its motion to and from 

 the cylinder is more free and rapid than in the condensing engine. 

 One half of the total power of the steam absorbed in the con- 

 densing engine, or out of seventeen pounds total pressure, only 

 seven pounds are made available for useful effect; while with 

 the high pressure engine, properly constructed, only one fourth 

 need be so consumed. The use of the high pressure steam allows 

 the principle of expansion to be carried to a greater extent than 

 in the low pressure engine, without requiring the dimensions of 

 the cylinder to be greatly increased. Watt could not carry out 

 this principle in low pressure engines, and Woolf, who re-intro- 

 duced it, used high pressure steam in his engines. Steam acts in 

 a positive manner, and is not robbed of all that valuable portion 

 of heat which in the low pressure engine is lost by condensation. 

 On this account, steam, from a high pressure engine, may be used 

 again for many purposes, such as warming the feed water before 

 it enters the boiler; for the purposes of cooking, heating build- 

 ings &c., free of cost. 



Steam, at a high temperature, is more exposed to condensation 

 than when at a lower degree of heat, since the transmission of 

 caloric from one body to another is quicker, as the difference 

 between their temperatures is greater. I think I have shown a 

 great advantage to be derived from high pressure steam; con- 

 sidered in respect to the economy of its production, and that the 

 advantage increases with the pressure employed. 



The principal objections against it are : First, it is asserted 

 that vessels, whenever high pressure steam is generated and con- 

 tained, must be more liable to burst, than such as are used for 

 low pressure. 



This proposition seems intelligible and self-evident to those 

 unskilled in such matters; yet it is only true in a qualified sense. 

 I would ask whether high pressure boilers have been found more 

 liable to explosion than low pressure. 



No instances have ever occurred where a destructive explosion 

 has happened to the engine itself, even to those worked to the 



