APPENDIX B. 259 



der with a piston, or in any other variable space; 

 finally, to throw it out again into the atmosphere, 

 or even to make it pass under a steam-boiler in 

 order to utilize the temperature remaining. 



The principal difficulties that we should meet in 

 this mode of operation would be to enclose the fur- 

 nace in a sufficiently strong envelope, to keep the 

 combustion meanwhile in the requisite state, to 

 maintain the different parts of the apparatus at a 

 moderate temperature, and to prevent rapid abra- 

 sion of the cylinder and of the piston. These dif- 

 ficulties do not appear to be insurmountable. 



There have been made, it is said, recently in 

 England, successful attempts to develop motive 

 power through the action of heat on atmospheric 

 air. We are entirely ignorant in what these at- 

 tempts have consisted if indeed they have really 

 been made. 



NOTE J. The result given here was furnished by 

 an engine whose large cylinder was 45 inches in 

 diameter and 7 feet stroke. It is used in one of the 

 mines of Cornwall called Wheal Abraham. This 

 result should be considered as somewhat excep- 

 tional, for it was only temporary, continuing but a 

 single month. Thirty millions of Ibs. raised one 

 English foot per bushel of coal of 88 Ibs. is generally 

 regarded as an excellent result for steam-engines. 



