34 THE HISTORY OF [SECT. i. 



those of Blake and Emerson. He has, however, by considering the atmospheric 

 pressure as a gravitating weight, failed in giving a correct solution. 



One of his problems includes the weight of the moving parts of the engine ; and 

 he adds some useful practical formula for the statical equilibrium of engines for 

 raising water, with examples. 



In 1803, Mr. Banks gave some rules for the strength of engine beams, both for 

 wood and cast iron ; and also a description of a gauge for determining the state of 

 rarefaction in the cylinders and condensers of steam engines, in principle the same 

 as the common barometer, and differing from the ordinary condenser gauge by 

 having a cistern instead of a syphon for the mercury. His rules for the strength 

 of beams are, to find the relation between the pressure and breaking weight, and to 

 let the breaking weight exceed the pressure by six, eight, or ten times. 1 



1797. Dr. EDMUND CARTWRIGHT ; born 1742, died 1823. 



43. The simple and neat combination of Cartwright next claims attention, 

 and on more grounds than one. He attempted to condense the steam by means of 

 cold applied externally to the condenser ; it consisting of two metal cylinders lying 

 one within the other, and having cold water flowing through the inner one and 

 enclosing the outer one. By this construction, a very thin body of steam is 

 exposed to a very great quantity of cooling surface ; and, by placing the valve to 

 change the steam in the piston, a constant communication is at all times open 

 between the condenser and the cylinder, so that, whether the piston ascends or 

 descends, the condensation is always taking place. 



One of the chief objects of this arrangement was the opportunity it afforded of 

 substituting ardent spirit or alcohol, either wholly or in part, in the place of water, 

 for working the engine ; for as the fluid with which it is worked is intended to 

 circulate through the engine without mixture and very little loss, the using alcohol, 

 after the first supply, it was expected, would be attended with little or no expense. 

 The power obtained from alcohol, it was then imagined, would require only half 

 the fuel which was necessary to obtain the same power from water (see Sect, iv.) ; 

 and Cartwright proposed, in some cases, to apply this engine to a still, to obtain 

 mechanical power by the distillation of ardent spirit, so as to save the whole of the 

 fuel. 2 How he was to keep the engine in a workable state, and yet obtain a pure 

 spirit, neither he nor his friends seem to have considered. 



In order to reduce the friction of the piston, which, when fresh packed in the 

 common way, lays a very heavy load upon the engine, Cartwright made his solely 



1 Power of Machines, p. 103. Phil. Mag. vol. i. p. 3. 



