Chap, s.] Engine. 39* 



brafs valve on the top of a pipe opening into the boiler, 

 to let off the fteam when it is too ftrong. It is loaded 

 with lead, at the rate of one pound to an inch fquare ; 

 and when the fteam is nearly ftrong enough to keep it 

 t)pen, it will do for the working of the engine. 



/, the fnifting valve, by which the air is difcharged 

 from the cylinder each ftroke, which was admitted 

 with the injection, and would otherwife obftruct the 

 due operation of the engine. 



1 /, the cylinder-beams; which are ftrong joifts go- 

 ing through the houfe for fupporting the cylinder. 



v, the cylinder cap of lead, foldered on the top of 

 the cylinder, to prevent the water upon the pifton from 

 flaming over when it rifes too high. 



Wj the wafte-pipe, which conducts the fuperfluous 

 water from the top of the cylinder to the hot- well. 



x x, iron bars, called the catch-pins, fixed horizon- 

 tally through each arch head, to prevent the beam de- 

 fcending too low in cafe the chain mould break. 



yy y two ftrong wooden fprings, to weaken the blow 

 given by the catch-pins when the ftroke is too long. 



z z y two friction-wheels, on which the gudgeon or 

 center of the great beam is hungj they are the third 

 or fourth part of a circle, and move a little each way 

 as the beam vibrates. Their ufe is to diminifh. the 

 friction of the axis, which in fo heavy a lever, would 

 otherwife be very great. 



When this engine is to be fet to work, the boiler 

 muft be filled about three or four feet deep with wa- 

 ter, and a large fire made under it ; and when the 

 fteam is found to be of a fufficient ftrength by the 

 puppet-clack, then by thrufting back the fpanner, 

 which opens the regulator or fteam-cock, the fteam is 

 admitted into the cylinder, which raifes the pifton to 

 the top of the cylinder, and forces out all the air at 

 C c 4 the 



