772 EBPOKT— 1881. 



not oEly he 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 for 

 its formation and its action. That portion of the food which is not used for 

 growth or structural repair, acts strictly as fuel in the production of heat. Part 

 of that heat goes to the maintenance of the animal temperature, and the remainder 

 gives rise to mechanical action. The only analogy between the steam engine and 

 this lining 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 piu'ely electrical, is so much of that natiu'e that we can produce the same 

 effect by electricity. The conductive system of the nerves is also in harmony wath 

 our conception of an electrical arrangement. In fact, a description of the animal 

 machine so closely coincides with that of an electro-dynamic machine actuated by 

 thermo-electricity, that we may conceive them to be substantially the same thing. 

 At all e^'ents, the animal process begms with combustion and ends with electrical 

 action, or something so nearly allied to it as to differ only in Icind. And now 

 observe how superior the result is in natm-e's engine to what it is in om-s. Nature 

 only uses heat of low grrade, such as we find whoUy 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, notwithstanding the gi'eater availability of high grade temperature, the 

 quantity of work performed by the living engine, relatively 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 attainability 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 nature, and profit by the 

 excellence which is there displayed. 



But it is not alone in connection with a better utilization of the heat of 

 combustion that tliermo-electricity 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 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- 

 wliich we possess in the condensed and portable form of coal, but in regions more 

 favoured 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 772, 

 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 4,000 horses acting 

 for nearly 9 hoiu-s 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 duration of coal, we need have none as to the duration of the sun. We have 

 therefore only to consider whether we can divert to oiu- 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 expect to bring into subjection a very 

 considerable proportion of the 4,000 invisible horses which Science tells us are to 

 be found within every acre of tropical ground. 



