SCIENCE. 



531 



sun's rays for motive power. In our climate, it is true, 

 we shall never be able to depend upon sunshine for power, 

 nor need we repine on that account so long as we have 

 the preserved sunbeams which we possess in the con- 

 densed and portable form of coal, but in regions more 

 favored with sun and less provided with coal the case 

 would be different, The actual power of the sun's rays 

 is enormous, being computed to be equal to melting a 

 crust of ice 103 feet thick over the whole earth in a year. 

 Within the tropics it would be a great deal more, but a 

 large deduction would everywhere have to be made for 

 absorption of heat by the atmosphere. Taking all things 

 into account, however, we shall not be far from the truth 

 in assuming the solar heat, in that part of the world, to 

 be capable of melting. annually, at the surface of the 

 ground, a layer of ice 85 feet thick. Now let us see 

 what this means in mechanical effect. To melt 1 lb. of 

 ice requires 142.4 English units of heat, which, multiplied 

 by 77 2 > gives us 109,932 foot pounds as the mechanical 

 equivalent of the heat consumed in melting a pound of 

 ice. Hence we find that the solar heat, operating upon 

 an area of one acre, in the tropics, and competent to 

 melt a layer of ice 85 feet thick in a year, would, if fully 

 utilized, exert the amazing power of 4000 horses acting 

 for nearly nine hours every day. In dealing with the 

 sun's energy we could afford to be wasteful. Waste of 

 coal means waste of money and premature exhaustion of 

 coal beds. But the sun's heat is poured upon the earth 

 in endless profusion — endless at all events in a practical 

 sense, for whatever anxiety we may feel as to the dura- 

 tion of coal, we need have none as to the duration of the 

 sun. We have therefore only to consider whether we 

 can divert to our use so much of the sun's motive energy 

 as will repay the cost of the necessary apparatus, and 

 whenever such an apparatus is forthcoming we may ex- 

 pect to bring into subjection a very considerable propor- 

 tion of the 4000 invisible horses which science tells us 

 are to be found within every acre of tropical ground. 



But whatever may be the future of electricity as a prime 

 mover, either in a dominant or subordinate relation to 

 heat, it is certain to be largely used for mechanical pur- 

 poses in a secondary capacity, that is to say, as the off- 

 spring instead of the parent of motive power. The most 

 distinctive characteristic of electricity is that which we 

 express by the word "current," and this gives it great 

 value in cases where power is required in a transmissible 

 form. The term may be objected to as implying a motion 

 of translation analogous to the flow of a liquid through a 

 pipe, whereas the passage of electricity through a conductor 

 must be regarded as a wave-like action communicated from 

 particle to particle. In the case of a fluid current through 

 a pipe, the resistance to the flow increases as the square 

 of the velocity, while in the case of an electric current the 

 resistance through a given conductor is a constant propor- 

 tion of the energy transmitted. So far therefore as resis- 

 tance is concerned electricity has a great advantage over 

 water for the transmission of power. The cost of the 

 conductor will however be a grave consideration where the 

 length is great, because its section must be increased in 

 proportion to the length to keep the resistance the same. 

 It must also be large enough in section to prevent heat- 

 ing, which not only represents loss but impairs conductiv- 

 ity. To work advantageously on this system, a high elec- 

 tromotive force must be used, and this will involve loss by 

 imperfect insulation, increasing in amount with the length of 

 the line. For these reasons there will be a limit to the 

 distance to which electricity may be profitably conveyed, 

 but within that limit there will be wide scope for its em- 

 ployment transmissively. Whenever the time arrives for . 

 utilizing the power of great waterfalls the transmission of 

 power by electricity will become a system of vast impor- 

 tance. Even now small streams of water inconveniently 

 situated for direct application may, by the adoption of this 

 principle, be brought into useful operation. 



For locomotive purposes also we find the dynamo- 



electric principle to be available, as instanced in the very 

 interesting example presented in Siemens' electric rail- 

 way, which has already attained that degree of success 

 which generally foreshadows an important future. It 

 forms a combined fixed engine and locomotive system of 

 traction, the fixed engine being the generator of the 

 power and the electric engine representing the locomo- 

 tive. 



Steam power may both be transmitted and distrib- 

 uted, by the intervention of electricity, but it will labor 

 under great disadvantage when thus applied, until a thor- 

 oughly effective electric accumulator be provided, capable 

 of giving out electric energy with almost unlimited 

 rapidity. How far the secondary battery of M. Faure 

 will fulfill the necessary conditions remains to be seen, 

 and it is to be hoped that the discussions which may be 

 expected to take place at this meeting of the British As- 

 sociation will enable a just estimate of its capabilities to 

 be formed. The introduction of the Faure battery is at 

 any rate a very important step in electrical progress. It 

 will enable motors of small power, whatever their nature 

 may be, to accomplish, by uninterrupted action, the effect 

 of much larger machines acting for short periods, and by 

 this means the value of very small streams of water wiri 

 be greatly enhanced. This will be especially the case 

 where the power of the stream is required for electric 

 lighting, which, in summer, when the springs are low, 

 will only be required during the brief hours of darkness, 

 while in winter the longer nights will be met by a more 

 abundant supply of water. Even the fitful power of 

 wind, now so little used, will probably acquire new life 

 when aided by a system which will not only collect, but 

 equalize, the variable and uncertain power exerted by the 

 air. 



It would greatly add to the utility of the Faure battery 

 if its weight and size could be considerably reduced, for 

 in that case it might be applicable to many purposes of 

 locomotion. We may easily conceive its becoming avail- 

 able in a lighter form for all sorts of carriages on com- 

 mon roads, thereby saving to a vast extent the labor of 

 horses. Even the nobler animal that strides a bicycle, or 

 the one of fainter courage that prefers the safer seat of a 

 tricycle, may ere long be spared the labor of propulsion, 

 and the time may not be distant when an electric horse, 

 far more amenable to discipline than the living one, may be 

 added to the bounteous gifts which science has bestowed 

 on civilized man. 



In conclusion I may observe that we can scarcely suffi- 

 ciently admire the profound investigations which have re- 

 vealed to us the strict dynamical relation of heat and 

 electricity to outward mechanical motion. It would be a 

 delicate task to apportion praise amongst those whose la- 

 bors have contributed, in various degrees, to our present 

 knowledge ; but I shall do no injustice in saying that of 

 those who have expounded the modern doctrine of en- 

 ergy, in special relation to mechanical practice, the names 

 of Joule, Clausius, Rankine, and William Thomson, will 

 always be conspicuous. But up to this time our knowledge 

 of energy is almost confined to its inorganic aspect. Of 

 its physiological action we remain in deep ignorance, and 

 as we may expect to derive much valuable guidance from 

 a knowledge of Nature's methods of dealing with en- 

 ergy in her wondrous mechanisms, it is to be hoped that 

 future research will be directed to the elucidation of that 

 branch of science which as yet has not even a name, but 

 which I may provisionally term " Animal Energetics." 



The dark violet fluor-spar of Wolsendorf contains some 

 strongly odorous substance, the nature of which has not 

 hitherto been satisfactorily explained. From recent ex- 

 periments (described to the Berlin Chemical Society,) Herr 

 Low concludes that the smell is due to presence of fret 

 fluorine, arising on elevation of temperature through dis- 

 sociation of a small quantity of flouride, (probably eerie 

 fluoride). 



