INITIATORY FORCES. 157 



tain-peak, it has often been a very slight force that has determined 

 the patli it has taken, and which of two villages miles apart was to 

 be demolished by it. The fire-alarm system in our cities uses elec- 

 tricity as an initiatory motion : the hammers of the tower-bells are 

 worked by the descent of heavy weights wound up by manual power 

 from time to time and the store of energy contained in the elevated 

 masses is instantly made available by an electric current from the 

 central office simply freeing a detent and allowing the weight to fall. 

 Many other recent inventions for working railway-signals, looms, etc., 

 embody this principle. The magneto-electric machines, which are ex- 

 tensively employed in lighthouses and electro-plating factories, yield 

 electricity from the mechanical motion of a steam-engine. A small 

 permanent steel magnet is indispensable in the apparatus ; it induces 

 magnetism in soft-iron cores, and these again in others in an increas- 

 ing series. The power may be gigantic, and the magnet, were it not 

 inconvenient, might be as small as a cambric needle: yet without it 

 neither electricity nor light can be had. A similar illustration occurs 

 in the development of a current in a common galvanic battery : the 

 two pieces of different metals used, as zinc and copper, when quite 

 dry before being placed in the bath, if simply brought into contact 

 for a moment show opposite electric polarities which, if given a me- 

 chanical expression, would be a very small amount indeed. This mi- 

 nute force, only to be detected by the most delicate means, is the 

 necessary opening of the flood-gate of energy in a working battery. 

 And when light is desired from a group of powerful cells, it is first 

 requisite to use a small effort in bringing the poles together, and then 

 separating them at a short distance apart. The brilliant arc of light, 

 once across the chasm, can continue to span it ; but its force, although 

 so great, is unequal to leaping over it without help. These examples 

 show the importance of knowing the fit initiatory forces in processes 

 whereby one form of energy is sought to be converted into another. 

 It is probably for lack of such knowledge that at present we waste so 

 lamentable a quantity of heat, our commonest force, in changing it 

 into the more desirable form of electricity, light, and mechanical mo- 

 tion. In exceptionally favorable circumstances, steam-engines of the 

 best kind give but a fourth in work of the theoretical value of the 

 heat applied, and in obtaining an electric current from an engine fur- 

 ther loss occurs ; while the production in a thermo-battery of a cur- 

 rent from heat directly has never yet yielded as much as one-hundredih 

 of the force employed. 



A slight and well-aimed effort may not only free an immense mag- 

 azine of energy, but also give it a particular direction and pilot it into 

 one or. another of two entirely new seas. Hydrogen and oxygen gases 

 in separate receivers might remain tranquil and unchanged for ages, 

 and it depends upon the choice of the experimenter, when he wishes 

 to render their energy available, whether their intense chemical force 



