SCIENCE AND MAN 



99 



more especially if that merit should have been 

 previously overlooked, he makes ready room in 

 his recognition or his reverence. But no retro- 

 spect of scientific literature has as yet brought to 

 light a claim which can sensibly affect the posi- 

 tions accorded to two great Path-hewers, as the 

 Germans call them, whose names in relation to 

 this subject are linked in indissoluble association. 

 These names are Julius Robert Mayer and James 

 Prescott Joule. 



In his essay on " Circles," Mr. Emerson, if I re- 

 member rightly, pictured intellectual progress as 

 rhythmic. At a given moment knowledge is sur- 

 rounded by a barrier which marks its limit. It 

 gradually gathers clearness and strength, until, by- 

 and-by, some thinker of exceptional power bursts 

 the barrier and wins a wider circle, within which 

 thought once more intrenches itself. But the inter- 

 nal force again accumulates, the new barrier is in 

 its turn broken, and the mind finds itself surround- 

 ed by a still wider horizon. Thus, according to 

 Emerson, knowledge spreads by intermittent vic- 

 tories instead of progressing at a uniform rate. 



When Dr. Joule first proved that a weight of 

 one pound, falling through a height of V72 feet, 

 generated an amount of heat competent to warm 

 a pound of water one degree Fahrenheit, and that 

 in lifting the weight so much heat exactly disap- 

 peared, he broke an Emersonian " circle," re- 

 leasing by the act an amount of scientific energy 

 which rapidly overran a vast domain. Helmholtz, 

 Clausius, Thomson, Rankine, Regnault, Woods, 

 Favre, and other illustrious names, are associated 

 with the conquests since achieved and embodied 

 in the great doctrine known as the " Conservation 

 of Energy." This doctrine recognizes in the 

 material universe a constant sum of power made 

 up of items among which the most protean fluc- 

 tuations are incessantly going on. It is as if the 

 body of Nature were alive, the thrill and inter- 

 change of its energies resembling those of an 

 organism. The parts of the " stupendous whole " 

 shift and change, augment and diminish, appear 

 and disappear, while the total of which they are 

 the parts remains quantitatively immutable — im- 

 mutable, because when change occurs it is always 

 polar — plus accompanies minus, gain accompanies 

 loss, no item varying in the slightest degree with- 

 out an absolutely equal change of some other 

 item in the opposite direction. 



The sun warms the tropical ocean, converting a 

 portion of its liquid into vapor, which rises in the 

 air and is recondensed on mountain-heights, re- 

 turning in rivers to the ocean from which it came. 

 Up to the point where condensation begins an 



amount of heat exactly equivalent to the molecular 

 work of vaporization and the mechanical work of 

 lifting the vapor to the mountain-tops has disap- 

 peared from the universe. What is the gain corre- 

 sponding to this loss ? It will seem when mentioned 

 to be expressed in a foreign currency. The loss 

 is a loss of heat ; the gain is a gain of distance, 

 both as regards masses and molecules. Water 

 which was formerly at the sea-level has been 

 lifted to a position from which it can fall ; mole- 

 cules which had been locked together as a 

 liquid are now separate as vapor which can re- 

 condense. After condensation gravity comes in- 

 to effectual play, pulling the showers down upon 

 the hills, and the rivers thus created through 

 their gorges to the sea. Every rain-drop which 

 smites the mountain produces its definite amount 

 of heat ; every river in its course develops heat 

 by the clash of its cataracts and the friction of 

 its bed. In the act of condensation, moreover, 

 the molecular work of vaporization is accurately 

 reversed. Compare, then, the primitive loss of 

 solar warmth with the heat generated by the con- 

 densation of the vapor, and by the subsequent 

 fall of the water from cloud to sea. They are 

 mathematically equal to each other. No particle 

 of vapor was formed and lifted without being 

 paid for in the currency of solar heat ; no parti- 

 cle returns as water to the sea without the exact 

 quantitative restitution of that heat. There is 

 nothing gratuitous in physical Nature, no expen- 

 diture without equivalent gain, no gain without 

 equivalent expenditure. With inexorable con- 

 stancy the one accompanies the other, leaving no 

 nook or crevice between them for spontaneity to 

 mingle with the pure and necessary play of natu- 

 ral force. Has this uniformity 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 illustration from chem- 

 istry. The metal zinc may be burned in oxy- 

 gen, a perfectly definite amount of heat being 

 produced by the combustion of a given weight of 

 the metal. But zinc may also be burned in a 

 liquid which contains a supply of oxygen — in 

 water, for example. It does not in this case pro- 

 duce flame or fire, but it does produce heat which 

 is capable of accurate measurement. But the 

 heat of zinc burned 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 per- 

 formance of this molecular work that the missing 



