10 THE SCIENTIFIC PAPERS OF 



The two condensers are cast in one piece, and placed immediately 

 in front of the cylinders of the engine. Each of them closely resembles 

 the condensers above described ; only the length of the condensing 

 plates and the stroke of the displacing pistons are much reduced 

 in proportion to the steam cylinder stroke, in order that the 

 velocity of the water between the plates may not exceed certain 

 limits. The two displacing pistons are connected to opposite ends 

 of a short vibrating beam, which receives its motion from the 

 engine. 



In addition to the exhaust valves leading into the hot well, 

 these condensers are provided with a second set of discharge 

 valves, of a somewhat peculiar construction, which with very 

 limited motion combine the advantage of opening a perfectly 

 clear passage for the exhaust steam of the engine into the chimney, 

 where its remaining expansive force is required to produce the 

 draught. Each' of these valves consists of a longitudinal rectan- 

 gular slot, in the upper wall of the steam passage which leads from 

 the cylinder to the condenser. At the ends of the slot are trian- 

 gular pieces, supporting the sides of two longitudinal lips which 

 cover the aperture, except at times when a higher pressure from 

 within forces them open : the extent of their motion is limited by 

 dead stops. The escape of steam, together with the hot water, 

 into the hot well is regulated by a blow-off valve from the hot well 

 into the atmosphere ; by this means a pressure above the atmos- 

 phere is obtained in the hot well, which acts favourably in forcing 

 the boiling-hot condensing water into the feed pump of the 

 boiler. 



It has been shown previously that the ordinary supply of feed 

 water in locomotive engines, where two-thirds of the steam is 

 allowed to escape uncondensed, is of itself not quite half-sufficient 

 to maintain a vacuum within the condenser, and an additional 

 supply of water must be provided for. But considering how 

 small the excess of condensing water will be, especially if the 

 diameters of the working cylinders are reduced in proportion 

 to the additional effective power gained, and considering that 

 boiling-hot water will readily part with the principal portion of 

 its heat, it is proposed to take the excess of condensing water back 

 to the tender through a simple refrigerator, in which advantage is 

 taken of the rapid motion of the engine through the air for 



