126 THE WATT AND THE TREVITHICK ENGINES. 



and under too light a load to do good duty ; also on a bad con- 

 struction, for the fly-wheel was loaded on one side, so as to divide 

 the power of the double engine, and connected to the pump-rods 

 on a very bad plan. I remember that Boulton and Watt's 20-inch 

 cylinders when on trial did not exceed ten millions ; I believe 

 you have the figures in your keeping. Let us have the 

 GO-horse power at work that is now building, and then I will 

 show what is to be done. It will be loaded at 30 Ibs. to the 

 inch on each side the piston, it has an 8-feet stroke with an 

 expansive cock, and the blowing cylinder directly over the 

 steam-cylinder, as free from friction as possible. There was no 

 engine stopped on account of this accident ; but I shall never 

 let the fire come in contact again with the cast iron. The 

 boiler at Greenwich was heated red hot and burnt all the joints 

 the Sunday before the explosion. 



" I have received a letter from a person in Staffordshire who 

 has a cylinder-boiler at work with the fire in it, and he says the 

 engine performs above all expectation ; he requests me to give 

 him leave to build a great many more. I shall put two steam- 

 valves and a steam-gauge in future, so that the quicksilver shall 

 blow out in case the valve should stick, and all the steam be 

 discharged through the gauge. A small hole will discharge a 

 great quantity of steam at that pressure. There will be a rail- 

 road-engine at work here in a fortnight ; it will go on rails not 

 exceeding an elevation of one-fiftieth part of a perpendicular 

 and of considerable length. The cylinder is 8J inches in dia- 

 meter, to go about two and a half miles an hour ; it is to have 

 the same velocity of the piston-rod. It will weigh, water and 

 all complete, within 5 tons. 



" I have desired Captain A. Yivian to wait on you to give you 

 every information respecting Murdoch carriage, whether the large 

 one at Mr. Budge's foundry was to be a condensing engine or not. 



" Is it possible that this engine might be burst by gas ? 

 I am, Sir, 



" Your very obedient servant, 



" KICHARD TREVITHICK." 



