CHAP. XIII. DISCUSSIONS OF THE STEPHENSONS. 261 



During the progress of the above important discussion 

 with reference to the kind of power to be employed in 

 working the railway, Mr. Stephenson was in constant 

 communication with his son Robert, who made frequent 

 visits to Liverpool for the purpose of assisting his father 

 in the preparation of his reports to the board on the 

 subject. Mr. Swanwick remembers the vivid interest 

 of the evening conversations which took place between 

 father and son as to the best mode of increasing the 

 powers and perfecting the mechanism of the locomotive. 

 He wondered at their quick perception and rapid judg- 

 ment on each other's suggestions, at the mechanical 

 difficulties which they anticipated and provided for 

 in the practical arrangement of the machine ; and he 

 speaks of these evenings as most interesting displays 

 of two actively ingenious and able minds, stimulating 

 each other to feats of mechanical invention, by which it 

 was ordained that the locomotive engine should become 

 what it now is. These discussions became more fre- 

 quent, and still more interesting, after the public prize 

 had been offered for the best locomotive by the directors 

 of the railway, and the working plans of the engine 

 which they proposed to construct had to be settled. 



One of the most important considerations in the new 

 engine was the arrangement of the boiler and the ex- 

 tension of its heating surface to enable steam enough to 

 be raised rapidly and continuously, for the purpose of 

 maintaining high rates of speed, the effect of high- 

 pressure engines being ascertained to depend mainly 

 upon the quantity of steam which the boiler can gene- 

 rate, and upon its degree of elasticity when produced. 

 The quantity of steam so generated, it will be obvious, 

 must chiefly depend upon the quantity of fuel consumed 

 in the furnace, and, by necessary consequence, upon the 

 high rate of temperature maintained there. 



It will be remembered that in Stephenson' s first 

 Killing worth engines he invented and applied the inge- 



