TKANSACTIONS OF SECTION G. 771 



■call fuel, of which coal is the most important, and, on the other, of oxygen, which 

 we derive from the atmosphere. The oxygen has an immense advantage over every 

 other available suhstance in being omnipresent and costless. The only money value 

 involved is that of the fuel, and in using coal we employ the cheapest oxidizable 

 substance to be found in nature. Moreover the weight of coal used in the 

 combination is only about one-third of the weight of oxygen, so that we only 

 pay upon one-fourth of the whole material consumed. Thus we have conditions 

 of the most favourable description for the production of energy, in the form of 

 heat, and if we could only use the affinities of the same substances with equal 

 facility to evolve electric energy instead of heat energy, there would be nothing 

 more to desire; but as yet there is no appearance of our being able to do this. 

 According to our present practice we consume zinc, instead of coal, in the voltaic 

 production of electricity, and not only is zinc 30 or 40 times dearer than coal but 

 it requires to be used in about sixfold larger quantity in order to develop an 

 equal amount of energy. Some people are bold enough to say that with our 

 present imperfect knowledge of electricity we have no right" to condemn all 

 plentiful substances, other than coal, as impractical substitutes for metallic 

 zinc, but it is manifest that we cannot get energy fi-om affinity, where affinity 

 has already been satisfied. The numerous bodies wliich constitute tlie mass of 

 our glolje, and which we call earths, are bodies in this inert condition. They 

 have already, by the union of the two elements composing them, evolved the 

 f"nergy due to combination, and that energv' has ages ago been dissipated in space 

 in the form of heat, never again to be available to us. As well might we try to 

 make fire witli ashes as to use such bodies over again as sources of either lieat or 

 electricity. To make them fit for our pui-pose we should first have to annul tlieir 

 state of combination, and this would require the expenditure of more energy upon 

 them than we could derive from their recombination. Water, being oxidized 

 hj-drogen, must be placed in the same category as the earths. In short, tlie onlv 

 abundant substances in nature possessing strong unsatisfied affinities are those of 

 organic origin, and in the absence of coal, which is the accumulated product of a 

 past vegetation, our supply of sucli substances would be insignificant. This beiu"- 

 the case, until a means be found of making the combination of coal with oxvgen 

 directly available for the development of electric energy, as it now is of heat 

 energy, there seems to be no probability of our obtaining electricity from chemical 

 action at such a cost as to supplant heat as a motive agent. 



But while still looking to heat as tlie fountain-head of our power, we mav very 

 possibly learn to transmute it, economically, into the more available form of 

 electricity. One method of transformation we already possess, and we have every 

 reason to believe there are otliers yet to be discovered. We know that when 

 dissimilar metals are joined at opposite ends, and heated at one set of junctions 

 while tliey are cooled at the otlier, part of the heat applied disappears in the 

 process, and assumes the form of an electric current. Each couple of metals may 

 be treated as the cell of a voltaic battery, and we may multiply them to any 

 extent, and group them in series or in parallels, with the same results as are 

 obtained by similar combinations of voltaic cells. The electricity so produced we 

 term Thermo-electricity, and the apparatus by which the current is evolved is the 

 thermo-electric battery. At present this apparatus is even more wasteful of heat 

 tlian the steam engine, but considering the very recent origin of this branch of 

 electrical science, and our extremely imperfect knowledge of the actions involved, 

 we may reasonably regard tlie present thermo-electi-ic batterv as the infant 

 condition of a discovery, which, if it follow the rule of all previous discoveries 

 in electricity, only requires time to develop into great practical importance. Now 

 if we possessed an efficient apparatus of this description we could at once apply 

 it to the steam engine for the pui-pose of converting into electric energy the heat 

 which now escapes with the rejected steam, and the gases from the fire. The vice 

 of the steam engine lies in its "inability to utilize heat of comparatively low grade 

 "but if we could use up tlie leavings of the .steam engine by a supplemental machine 

 acting on thermo-electric principles, the present excessive waste would he avoided. 

 We may even anticipate that in the distant future a thermo-electric engine may 



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