VARIOUS INVENTIONS. 



of its course : thus both these things were as first steps 

 leading to the modern expansive steam-engine and sur- 

 face condensation. 



The simplicity of the engine is remarkable a high- 

 pressure, expansive, condensing engine, worked by a 

 single four- way cock, without cylinder-cover, or parallel 

 motion. 



The low first cost, and non-liability to derangement, 

 were always kept in view; and his confirmed experi- 

 ence in the satisfactory working of horizontal cylinders 

 prior to 1812 illustrates their extended application ; 

 for at that time scarcely any other engineer had con- 

 structed other than upright cylinder engines. No detail 

 escaped his observant gaze. The fire-bars were to be 

 2 inches deep, 1 inch thick at the top edge, tapered to 

 fths of an inch at the bottom., giving the required 

 strength, with free room for air, which in its passage 

 cooled the bar, carrying the heat into the fire. Years 

 before and after that period the fire-bar in common use 

 by thoughtless people was a square iron bar that was 

 always burning and bending. 



The letter is descriptive of the high-pressure steam- 

 engine in the sixteenth year of its age ; and its expan- 

 sive steam, made practical by Ti evithick's high-pressure 

 boilers. This engine only took steam during the first 

 quarter of its stroke, the remaining three-quarters were 

 by the expansion. Had it taken steam only during one- 

 twentieth of its stroke, it would have been more power- 

 ful than Boulton and Watt's low-pressure steam vacuum 

 engine of the same size. 



[Rough draft.] 

 " SlR, " CAMBOKNE, November 8th, 1812. 



"I have your favour of the 3rd inst., informing me that 

 Messrs. Fox and Williams have engaged to quarry the stone for 



