DISCOURSE OF W. B. TAYLOR. 231 



changer or commutator ever applied to the galvanic battery, an 

 essential element not merely in every variety of the electro-magnetic 

 machine, but in every variety of magneto-electric apparatus, and in 

 every variety of the highly useful induction apparatus. 



In an interesting "Historical Sketch of the rise and progress 

 of Electro-magnetic Engines for propelling machinery ;" by the 

 distinguished philosopher James P. Joule, he remarks: "Mr. 

 Sturgeon's discovery of magnetizing bars of soft iron to a con- 

 siderable power, and rapidly changing their polarity by miniature 

 voltaic batteries, and the subsequent improved plan by Professor 

 Henry of raising the magnetic action of soft iron, developed 

 new and inexhaustible sources of force which appeared easily and 

 extensively available as a mechanical agent; and it is to the ingen- 

 ious American philosopher above named, that we are indebted for 

 the first form of a working model of an engine upon the principle 

 of reciprocating polarity of soft iron by electro-dynamic agency." : 



In Henry's deliberate contemplation of his own achievement, 

 his remarkable sagacity and sobriety of judgment were conspicu- 

 ously displayed. Unperturbed by the enthusiasm so natural to the 

 successful inventor, he carefully scanned the capabilities of this new 

 dynamic agent. Considering the source of the power, he arrived 

 at the conclusion that the de-oxidation of metal necessary for the 

 battery, would require the expenditure of at least as much power 

 as its combustion in the battery could refund; and that the coal 

 consumed in such de-oxidation could be much more economically 

 employed directly in the work to be done.f As the battery con- 

 sumption moreover was found to increase more rapidly than the 

 magnetic power produced, he was at once convinced that it could 



* Sturgeon's Annals of Electricity, etc. March, 1839, vol. iii. p. 430. STURGEON 

 himself the first to devise a rotary electro-magnetic engine, deserves honorable 

 mention for correcting the statement of an American writer, and declining his 

 mistaken award by frankly recognizing HENRY'S right to priority. (Annals of 

 Electricity, April, 1839, vol. iii. p. 554.) 



t These considerations have been more than justified by later comparative 

 investigations. RANKINE estimates that the consumption of one pound 'of zinc 

 will not produce more than one-tenth the energy that one pound of coal will ; 

 and that though in. the efficient utilization of this energy it is four times superior, 

 its useful work is therefore less than half that of coal; while its cost is from forty 

 to fifty times greater. (The Steam Engine and other Prime Movers. By W. J. M. 

 Rankine. London and Glasgow, 1859, part iv. art. 395, p. 541.) 



