185 



Surface Condenser. A three-horse power high-pressure steam- 

 engine was procured for our experiments. Wishing to give it equal 

 power with a lower pressure, we caused the steam from the eduction 

 port to pass downwards through a perpendicular iron gas-pipe, ten 

 feet long and an inch and a half in diameter, placed within a larger 

 pipe through which water was made to ascend. The lower end of 

 the gas-pipe was connected with the feed-pump of the boiler, a small 

 orifice being contrived in the pump cover in order to allow the 

 escape of air before it could pass, along with the condensed water, 

 into the boiler. This simple arrangement constituted a "surface 

 condenser" of a very efficient kind, giving a vacuum of 23 inches, 

 although considerable leakage of air took place, and the apparatus 

 generally was not so perfect as subsequent experience would have 

 enabled us to make it. Besides the ordinary well-known advantages 

 of the " surface condenser," such as the prevention of incrustation 

 of the boiler, there is one which may be especially remarked as 

 appertaining to the system we have adopted, of causing the current of 

 steam to move in an opposite direction to that of the water employed 

 to condense it. The refrigerating water may thus be made to pass 

 out of the condenser at a high temperature, while the vacuum is that 

 due to a low temperature ; and hence the quantity of water used for 

 the purpose of condensation may be materially reduced. We find 

 that our system does not require an amount of surface so great as to 

 involve a cumbrousness or cost which would prevent its general 

 adoption, and have no doubt that it will shortly supersede that at 

 the present time almost universally used. 



IV. " On the Stability of Loose Earth." By W. J. MACQUORN 

 RANKINE, Esq., C.E., F.R.SS. L & E., Regius Professor of 

 Civil Engineering and Mechanics in the University of 



Glasgow. 



(Abstract.) 



The object of this paper is to deduce the mathematical theory of 

 that kind of stability which depends on the mutual friction of the 

 parts of a granular mass devoid of tenacity, from the known laws of 

 friction, unaided by any hypothesis. 



