DESCRIPTION OF AS AIR ENGINE. g^l 



idea, as you justly remark, is by no meaps new in this 

 country; yet I have not heard that ^ny successful experi- 

 ments have been made, exclusively upon this principle, in 

 England, though you hint that something promising has 

 been accomplished relative to it. 



The subject is of much importance, as the steam engine its advantages* 

 has hitherto proved too v/eighty and cumbrous for most 

 purposes of locomotion ; whereas the expansion of air seems 

 calculated to supply a mover free from these defects. Under 

 this impression I send you a sketch of an engine I projected 

 upon this principle several years ago,^ it was made on a con- 

 siderable scale at Newcastle, though I must confess without 

 success in the result, which T attributed to the imperfect 

 iilanner in which it was executed, the cylinders being made 

 of sheets copper, and so irregular, as not to be rendered 

 tolerably air-tight bv any packing of the piston. I think 

 there can be no doubt that the scheme is practicable in some 

 way or other ; and I conceive that the form of the engine here 

 sketched will be the basis of whatever experience may prove 

 to be additional requisite to perfection in the apparatus of 

 the air engine. 



A and B, PI. VIIT, fig. 1, are two cylinders, placed one Description of 

 above another; C and D, their respective pistons connected an engine; 

 by one rod. F is a cylinder, containing a fire in a vessel btowhie cy^lir^ 

 within it in such a manner, that any air passing between the der & a work- 

 upper and lower portions of it must go through the fire. ^"^ '^^^'^ '^'^* 

 This vessel also contains a long cylinder, open at the bot- 

 tom, and directly over the centre of the fire, for the purpose 

 of holding coke or other fuel. This cylinder is covered at 

 the top, and packed air-tight when it has served the purpose 

 of permitting the fire to be kindled through it : and has been 

 filled with fuel. 



The cylinder B is fitted up to answer the purpose of a 

 double stroke forcing pump, or bellows, to drive the air into 

 the upper portion oi the vessel F, from whence it passes 

 downwards thi-ough the fire for the purpose of consuming 

 the smoke (the fresh fuel being supplied from the reservoir 

 above) in its passage through the more completely ignited ■ -^f*"^ 



cinders below. In this act the air is expanded; and, by 

 means of pipes from the low6r portion of F, it is conveyed 



alteriiately 



