SPEECH OF SIR WILLIAM ARMSTRONG. 377 



proved practical methods of converting the heat of comhustion 

 into available power. Engines in which the motive power is ex- 

 cited by the communication of heat to fluids already existing in 

 the aeriform condition, as in those of Sterling, Ericsson, and Sie- 

 mens, promise to afford results greatly superior to those obtained 

 from the steam-engine. They are all based upon the principle of 

 employing fuel to generate sensible heat, to the exclusion of latent 

 heat, which is only another name for heat which has taken the 

 form of unprofitable motion among the particles of fluid to which 

 it is applied. They also embrace what is called the regenerative 

 principle — a term which has, with reason, been objected to, as im- 

 plying a restoration of expended heat. The so-called " regenera- 

 tor " is a contrivance for arresting unutilized heat rejected by the 

 engine, and causing it to operate in aid and consequent reduction 

 of fuel. It is a common observation that before coal is exhausted 

 some other motive agent will be discovered to take its place, and 

 electricity is generally cited as the coming power. Electricity, 

 like heat, may be converted into motion, and both theory and prac- 

 tice have demonstrated that its mechanical application does not 

 involve so much waste of power as takes place in a steam-engine ; 

 but, whether we use heat or electricity as a motive power, we must 

 equally depend upon chemical affinity as the source of supply. 

 The act of uniting to form a chemical product liberates an energy 

 which assumes the form of heat or electricity, from either of which 

 states it is convertible into mechanical effect. In contemplating, 

 therefore, the application of electricity as a motive power we must 

 bear in mind that we shall still require to effect chemical combi- 

 nations, and in so doing to consume materials. But where are we 

 to find materials so economical for this purpose as the coal we 

 derive from the earth and the oxygen we derive from the air ? 

 The latter costs absolutely nothing ; and every pound of coal which 

 in the act of combustion enters into chemical combination renders 

 more than 2Jlbs. of oxygen available for power. "We cannot look 

 to water as a practicable source of oxygen, for there it exists in 

 the combined state, requiring expenditure of chemical energy for its 

 separation from hydrogen. It is in the atmosphere alone that it can 

 be found in that free state in which we require it ; and there does 

 appear to me to be the remotest chance, in an economic point of 

 view, of being able to dispense with the oxygen of the air as a 

 source either of thermodynamic or electrodynamic effect. But to 

 Can/ Nat. 25 Vol. VIII. 



