53Q 



SCIENCE. 



sun's rays, which as yet we have not succeeded in apply- 

 ing to motive purposes. Secondly we have water power, 

 wind power, and tidal power, all depending upon influ- 

 ences lying outside of our planet, And thirdly we have 

 chemical attraction or affinity. Beyond these there is 

 nothing worth naming. Of the radiant heat of the sun 

 I shall have to speak hereafter, and bearing in mind that 

 we are in search of electricity as a cause, and not an 

 effect, of motive power we may pass over the dynamical 

 agencies comprised under the second head, and direct 

 our attention to chemical affinity as the sole remaining 

 source of energy available for our purpose. At present 

 we derive motive power, from chemical attraction through 

 the medium of heat only, and the question is, can we with 

 advantage draw upon the same source through the me- 

 dium of electricity. The process by which we obtain 

 our supply of heat from the exercise cf affinity is that of 

 combustion, in which the substances used consist, on the 

 one hand, of those we 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 ad- 

 vantage over every other available substance in being 

 omnipresent and costless. The only money value in- 

 volved 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 con- 

 sumed. Thus we have conditions -of the most favor- 

 able 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 thirty or forty times 

 dearer than coal, but it requires to be used in about 

 six-fold larger quantity in order to develop an equal 

 amo'int 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 impracticable substitutes for metallic 

 zinc, but it is manifest that we cannot get energy from 

 affinity, where affinity has already been satisfied. The 

 numerous bodies which constitute the mass of our globe, 

 and which we call earths, are bodies in this inert condi- 

 tion. They have already, by the union of the two ele- 

 ments composing them, evolved the energy due to com- 

 bination, and that energy 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 with ashes, as to 

 use such bodies over again as sources of either heat or 

 electricity. To make them fit for our purpose, we should 

 first have to annul their state of combination, and this 

 would require the expenditure of more energy upon them 

 than we could derive from their recombination. Water, 

 being oxidized hydrogen, must be placed in the same 

 category as the earths. In short, the only abundant sub- 

 stances in nature possessing strong unsatisfied affini- 

 ties are those of organic origin, and in the absence of 

 coal, which is the accumulated product of a past vegeta- 

 tion, our supply of such substances would be insignifi- 

 cant. This being the case, until a means be found of 

 making the combination of coal with oxygen 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 the fountain-head of 

 our power, we may 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 others yet to 

 be discovered. We know that when dissimilar metals 



are joined at opposite ends, and heated at one set of 

 junctions while they are cooled at the other, 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 ob- 

 tained by similar combinations of voltaic cells. The elec- 

 tricity 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 than the steam-engine, but considering 

 the very recent origin of this branch of electrical science, 

 and our extremely imperfect knowledge of the actions in- 

 volved, we may reasonably regard tne present thermo- 

 electric battery 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 prac- 

 tical importance. Now if we possessed an efficient ap- 

 paratus of this description we could at onCe apply it to 

 the steam-engine for the purpose of converting into elec- 

 tric energy the heat which now escapes with the re- 

 jected steam, and the gases from the fire. The vice of 

 the steam-engine lies in its inability to utilize heat of com- 

 paratively low grade, but if we cculd use up the leavings 

 of the steam-engine by a supplemental machine acting on 

 thermo-electric principles, the present excessive waste 

 would be avoided. We may even anticipate that in the 

 distant future a thermo-electric engine may not only be 

 used as an auxiliary, but in complete substitution of the 

 steam-engine. Such an expectation certainly seems to 

 be countenanced by what we may observe in animated 

 nature. An animal is a living machine dependent upon 

 food both lor its formation and its action. That portion 

 of the food which is not used for growth or structural re- 

 pair, acts strictly as fuel in the production of heat. Part 

 of that heat goes to the maintenance of the animal tem- 

 perature, and the remainder gives rise to mechanical ac- 

 tion. The only analogy between the steam engine and 

 this living engine is that both are dependent upon the 

 combustion of fuel, the combustion in the one case being 

 extremely slow, and in the other very rapid. In the steam- 

 engine the motion is produced by pressure, but in the 

 animal machine it is effected by muscular contraction. 

 The energy which causes that contraction, if not purely 

 electrical, is so much cf that nature that we can produce 

 the same effect by electricity. The conductive system of 

 the nerves is also in harmony with our conception of an 

 electrical arrangement. In fact a description of the 

 animal machine so closely coincides with that of an elec- 

 tro-dynamic machine actuated by thermo-electric'ty, 

 that we may conceive them to be substantially the same 

 thing. At all events, the animal process begins with 

 combustion and ends with electrical action, or something 

 so nearly allied to it as to differ only in kind. And now 

 observe how superior the result is in nature's engine to 

 what it is in ours. Nature oniy uses heat of low grade, 

 such as we find wholly unavailable. We reject our steam 

 as useless at a temperature that would cook the animal 

 substance, while nature works with a heat so mild as not 

 to hurt the most delicate tissue. And yet, notwithstand- 

 ing the greater availability of high-grade temperature the 

 quantity of work performed by the living engine rela- 

 tively to the fuel consumed, puts the steam-engine to 

 shame. How all this is done in the animal organization 

 we do not yet understand, but the result points to the at- 

 tainability of an efficient means of converting low-grade 

 heat into electricity, and in striving after a method of 

 accomplishing that object we shall do well to study na- 

 ture, and profit by the excellence which is there displayed. 



But it is not alone in connection with a better utiliza- 

 tion of the heat of combustion that thermo-electric ty 

 bears so important an aspect, for it is only the want of 

 an efficient apparatus for converting heat into electricity 

 that prevents our using the direct heating action of the 



