Perkins' Steam Engine. 47 



imum pressure of steam, which is equal to about 4000 atmos- 

 pheres, when the water is heated to about 1200°. That 

 pressure would, I believe, keep it in contact with iron at any 

 degree of heat, and the steam would then be as dense as wa- 

 ter. It is very evident that if it would require that force to 

 keep the water in contact, heated as it was at the vent 

 hole, thirty atmospheres must be insufficient to effect this : 

 but the experiment affords some data towards answering the 

 question, at what distance from the heated metal the water 

 remained, when under the pressure of thirty atmospheres ? 

 We may safely aver, that it exceeded one-eighth of an inch, 

 as the hole was one quarter of an inch in diameter. 



After commencing this letter, I ascertained that my patent 

 was likely in a few days to pass the great seal, and have de- 

 layed forwarding it until I could give you some account of 

 the effect upon the minds of those engineers who were open 

 to conviction, of an experiment performed before them. 

 The patent has been sealed, and the engine has had its pow- 

 er and economy tested. The result has been so satisfactory, 

 that an engineer, who employs at least three hundred hands, 

 has taken orders to make engines, (for I license them out,) 

 with the following guarantee, viz. that of saving half the fuel, 

 and three-fourths of the weight and bulk, with less liability of 

 derangement than ordinary engines. The engineer whose 

 name is Penn, and who is frequently employed by govern- 

 ment, is now making an engine for steam navigation, with a 

 nine inch cylinder, and twenty inch stroke ; he joins me in 

 guaranteeing it to be of sixty horse power. It will not oc- 

 cupy more than one-sixth of the room, nor exceed one-sixth 

 of the weight, of the ordinary Boulton and Watt's engine, 

 of the same power. 



I have sent you the last " London Journal of Arts, &c." 

 which contains some account of my engine, which is nearly 

 correct as far as it goes. It should however have stated, 

 that the piston was eight inches in diameter, that it was a 

 twenty inch single stroke engine, a good seventy horse power 

 and consuming but one-fourth of the coal of a condensing 

 engine. The weight on the end of the lever was three hun- 

 dred, instead of one hundred and fifty pounds. 



You may, my dear sir, depend upon what I have written ; 

 it is the result of actual experiment, and there is no fallacy 

 in it. Having succeeded in making a piston which requires 

 no oil, I am determined to ascertain the limits to which pres- 



