20 ANNUAL OF SCIENTIFIC DISCOVERY. 



ing cylinder and heater, slovr combustion is kept up, until the heaters 

 and lower parts of the regenerators are at a temperature of about 500 

 Fah. By means of a hand-pump, atmospheric air is then forced into the 

 receiver, until there is an internal pressure of 8 or 10 pounds to the 

 inch. A communication is then opened with the working cylinder, 

 the piston rises, and the air in the upper cylinder is forced into the 

 receiver ; other valves then open, so that the air passes through the 

 wire regenerators, and has its temperature augmented. Before the piston 

 arrives at the top of the up stroke, the valve which first opened will be 

 closed, and another opened, causing the down stroke, when the air 

 passes through the cooled regenerator and escapes, deprived nearly of 

 all its caloric. The air next passing takes up the caloric so deposited ; 

 and thus a continuous reciprocating motion is kept up. The specifica- 

 tion goes on to say, that, after a certain number of strokes, the temper- 

 ature of the regenerators will change the cooler one gradually 

 gaining an increase of temperature, while the hottest gradually gets 

 cooler ; and, therefore, the position of the slide valves is reversed at 

 about every fifty strokes by a self-acting arrangement, which can be 

 regulated as desired. 



It is proper to observe that the small cylinder only receives and trans- 

 mits the differential force of the piston of the large cylinder, viz., the 

 excess of its acting force over the reacting force of the piston of the 

 small cylinder. This differential force imparted to said piston rod may 

 be communicated to machinery by any of the ordinary means. It is 

 particularly worthy of notice, that the relative diameter of the supply 

 and working, or larger and smaller cylinder, will depend on the expan- 

 sibility of the acting medium employed ; thus, in using atmospheric air, 

 or other permanent gases, the difference of the area of the pistons may 

 be nearly as two to one ; while, in using fluids, such as oils, which 

 dilate but slightly, the difference of area should not much exceed one 

 tenth. 



An engine of the above description was exhibited by Captain Erics- 

 son, at the Great London Exhibition, and has since, we understand, 

 been working in New York. 



HOT-AIR ENGINE. 



A PAPER has been recently read before the Institution of Civil En- 

 gineers, London, respecting a hot-air engine invented by Sir G. Cay- 

 ley. After entering briefly into the theoretical considerations of the 

 expansion of aeriform bodies, and detailing the attempts made by Capt. 

 Ericsson for employing hot air, instead of steam, as a prime mover, the 

 author proceeded to state, that Sir G. Cayley applied the products of 

 combustion from close furnaces so that they should act at once upon a 

 piston, in a cylinder, similar in every respect to that of a single acting 

 steam engine. The engine consisted of a generator of heat, a working 

 cylinder, and an air-pump or blower the air-pump being half the size 

 of the cylinder, and blowing air into and through a fire perfectly in- 

 closed within the generator. The doors of the furnace were made per- 

 fectly air-tight as soon as the fire was well got up ; the first impulse 

 being given to the engine by throwing a few jets of water upon the 



