So 



LECTURES AND ESS A YS 



of nature ever been broken ? The reply 

 is : " Not to the knowledge of science." 



What has been here stated regarding 

 heat and gravity applies to the whole of 

 inorganic nature. Let us take an illus- 

 tration from chemistry. The metal zinc 

 may be burnt in oxygen, a perfectly 

 definite amount of heat being produced 

 by the combustion of a given weight of 

 the metal. But zinc may also be burnt 

 in a liquid which contains a supply of 

 oxygen in water, for example. It does 

 not in this case produce flame or fire, 

 but it does produce heat which is capable 

 of accurate measurement. But the heat 

 of zinc burnt in water falls short of that 

 produced in pure oxygen, the reason 

 being that to obtain its oxygen from the 

 water the zinc must first dislodge the 

 hydrogen. It is in the performance of 

 this molecular work that the missing heat 

 is absorbed. Mix the liberated hydrogen 

 with oxygen and cause them to recom- 

 bine ; the heat developed is mathemati- 

 cally equal to the missing heat. Thus, in 

 pulling the oxygen and hydrogen asunder 

 an amount of heat is consumed which is 

 accurately restored by their reunion. 



This leads up to a few remarks upon 

 the Voltaic battery. It is not my design 

 to dwell upon the technical features of 

 this wonderful instrument, but simply, 

 by means of it, to show what varying 

 shapes a given amount of energy can 

 assume while maintaining unvarying 

 quantitative stability. When that form 

 of power which we call an electric cur- 

 rent passes through Grove's battery, zinc 

 is consumed in acidulated water ; and in 

 the battery we are able so to arrange 

 matters that when no current passes no 

 zinc shall be consumed. Now the cur- 

 rent, whatever it may be, possesses the 

 power of generating heat outside the 

 battery. We can fuse with it iridiuin, 

 the most refractory of metals, or we can 

 produce with it the dazzling electric light, 

 and that at any terrestrial distance from 

 the battery itself. 



We will now, however, content our- 

 selves with causing the current to raise a 

 given length of platinum wire, first to a 



blood-heat, then to redness, and finally 

 to a white heat. The heat under these 

 circumstances generated in the battery 

 by the combustion of a fixed quantity of 

 zinc is no longer constant, but it varies 

 inversely as the heat generated outside. 

 If the outside heat be nit, the inside heat 

 is a maximum ; if the external wire be 

 raised to a blood-heat, the internal heat 

 falls slightly short of the maximum. If 

 the wire be rendered red-hot, the quantity 

 of missing heat within the battery is 

 greater, and if the external wire be ren- 

 dered white-hot the defect is greater 

 still. Add together the internal and 

 external heat produced by the combus- 

 tion of a given weight of zinc, and 

 you have an absolutely constant total. 

 The heat generated without is so much 

 lost within, the heat generated within is 

 so much lost without, the polar changes 

 already adverted to coming here con- 

 spicuously into play. Thus in a variety 

 of ways we can distribute the items of a 

 never-varying sum, but even the subtle 

 agency of the electric current places no 

 creative power in our hands. 



Instead of generating external heat, 

 we may cause the current to effect 

 chemical decomposition at a distance 

 from the battery. Let it, for example, 

 decompose water into oxygen and hydro- 

 gen. The heat generated in the battery 

 under these circumstances by the com- 

 bustion of a given weight of zinc falls 

 short of what is produced when there is 

 no decomposition. How far short ? The 

 question admits of a perfectly exact 

 answer. When the oxygen and hydrogen 

 recombine, the heat absorbed in the de- 

 composition is accurately restored, and it 

 is exactly equal in amount to that missing 

 in the battery. We may, if we like, 

 bottle up the gases, carry in this form 

 the heat of the battery to the polar 

 regions, and liberate it there. The 

 battery, in fact, is a hearth on which 

 fuel is consumed ; but the heat of the 

 combustion, instead of being confined 

 in the usual manner to the hearth itself, 

 may be first liberated at the other side of 

 the world. 



