July 2, 1894.] 



KNOWLEDGE. 



1G5 



equivalent " is constant — that is to say, tlie amount of 

 mechanical effect it would produce if the energy were 

 all converted into the motion of a mass of matter. In 

 Nature nothing is lost ! Surely no dictum of science was 

 ever more contrary to the voice of common sense — that is 

 to say, the sense of what is reasonable derived from the 

 ordinary experience of life. 



Let us take first the law of conservation of mass. It has 

 been the common experience of mankind for ages that 

 solid fuel burns away, producing a certain amount of 

 smoke and leaving a little ash behind, no other substance 

 being formed in the burning. There is nothing else 

 produced which is either visible, tangible, or, as far as 

 common experience goes, ])onderable. Common experience 

 failed to afford an insight into the changes in the forms 

 of matter which happen during burning. Lavoisier's 

 FJ.rpt'i'iences {vide Knowledcje, February, 1892) corrected 

 common sense in this, and we now say that in chemical 

 changes no matter is destroyed. Common experience tells 

 us, however, that things have a tendency to wear out and 

 get used up — iron rusts, for instance, and soil loses its 

 fertility. Later chemical research has confirmed this 

 common experience, and shows that the general tendency 

 of chemical changes is to the production of material 

 less capable of reacting chemically, and therefore less 

 available for the work of the world. The carbon chemi- 

 cally combined in plants is still capable of burning, and as 

 a constituent of vegetable food is converted by animals into 

 carbonic acid. Certainly no carbon has been annihilated, 

 but when it has got to the final form of carbonic acid 

 there is little more that carbon can do. If it is not lost, 

 it is at all events pretty securely locked up. Were it not 

 for the extraneous energy the earth receives from the 

 sun's rays, the carbon in carbonic acid would be, in this 

 sense, irretrievably lost. In the processes of industrial 

 chemistry we may often see the manufacturer's art applied 

 to the production of some material in a form in which it is 

 chemically active ; we may cite, for instance, iron-smelting 

 and alkali-making. Dwellers in the neighbourhood of 

 Middlesborough, or of Widnes, realize better than most 

 people that for every ton of iron a far greater 'quantity of 

 an eft'ete slag is formed — slag which has accumulated in 

 masses greater than the pyramids of Egypt — and that for 

 every ton of soda there are produced nearly two tons of 

 alkali waste. 



The balance of chemical change is on the side of 

 diminished chemical activity. Nature grows weary, and 

 protests afterwards against changes which she does not 

 prevent, and often scarcely hindered at the time. 



It is, however, in the domain of physics rather than in 

 chemistry, in transformations of energy more than in 

 transformations of matter, that Nature's protest against 

 change is most strikingly shown. We do not refer merely 

 to the property of mertia, in Virtue of which all bodies 

 resist a change in their state of rest or motion. In this 

 case, if the resistance be overcome and the motion of the 

 body be increased, energy is stored up in the increased 

 momentum of the body ; but when such exchanges of 

 energy are examined in detail there always appears a 

 residual phenomenon which mars the simplicity and com- 

 pleteness of the result. Take the case of any of the 

 well-known mechanical appliances. A small force is made 

 to raise a large weight, and if we multiply the force by the 

 distance through which its point of application is moved 

 the product would be equal to that of the w eight multiplied 

 by the distance wliich the weight is raised, were it not for 

 the inevitable friction which fritters away a part of the 

 mechanical energy in the less available form of heat. It 

 is true that the heat so produced has its mechanical 



equivalent. Heat can be converted into mechanical work, 

 and one unit of heat converted into mechanical energy 

 produces one thousand three hundred and ninety foot 

 pounds, the same amount of mechanical work which waa 

 required to produce the unit quantity of heat ; but if we 

 are dealing with the unit quantity of heat, it is found in 

 practice to be impossible to transform the whole of it into 

 mechanical worlc. Part still remains in the form of heat. 

 Perhaps one half of the unit quantity of heat may be con- 

 verted into six hundred and ninety-five foot pounds, leaving 

 the other half still in the form of heat energy. This is an 

 example of the conservation of heat energy, but it is a 

 somewhat unsatisfactory form of conservatism, for the half 

 unit of heat which is left is heat at a lower temperature or 

 heat-level than that with which we started, and is less 

 available for further transformation. Only a reduced 

 proportion of this heat can be converted into the higher or 

 more available forms of energy. Hirn's experiments with 

 the steam engine illustrate this point. The loss of heat 

 between the boiler and condenser is accounted for by the 

 mechanical work done, and the mechanical equivalent of 

 heat determined in this way is identical with the heat 

 equivalent of work determined by Joule's method of 

 warming a liquid by the friction of paddle-wheels driven 

 by a falhng weight. But the steam engine cannot be 

 worked without a transference of heat between the boiler 

 and the condenser, over and above the heat that is used to 

 overcome resistance. This surplus heat is degraded from 

 the high temperature of the boiler to the low temperature 

 of the condenser. It is still the same in quantity, but it 

 is less available for transformation, less ready to undergo 

 further change. In this case of the running down or 

 degradation of energy an external mechanical effect is 

 produced, and the result is in accordance with our every- 

 day experience, and therefore is consistent with the 

 expectations of common sense. We cannot work without 

 growing tired, and it does not seem unreasonable that 

 something analogous to fatigue should be shown by 

 inorganic nature. But the inorganic world shows loss of 

 vigour, not only after effort, but after any change, even 

 though not accompanied by external effect. It is in such 

 phenomena of diminished vigour, resultmg from all those 

 natural changes which proceed without effort and without 

 the accomplishment of work, that we best see Nature's 

 protest against all change. One of the best illustrations, 

 which is not only a striking one, but has been carefully 

 and quantitatively examined, is afforded by the expansion 

 of compressed air into a vacuum. In Joule's well-known 

 experiments, a vessel containing compressed air and 

 provided with a stop- cock was attached to a similar vessel 

 which had been exhausted of air. The two were placed in 

 the same vessel of water, and the temperature carefully 

 noted. The stop-cock was then opened, and the compressed 

 air was allowed to rush into the empty vessel. The empty 

 vessel is thereby heated, and the full vessel cooled ; but on 

 stirring the water of the outer or containing vessel so 

 as to equalize the temperatures throughout, it is found 

 that the temperature of the system of bodies has, as 

 a whole, undergone no alteration. The only change 

 is that the energy of the air is less available than 

 it was before. There is the same amount of energy 

 in it, but in order to get energy out of it we should 

 have to expend work upon it, e.;/., by compressing 

 it again into a smaller space. A similar and even more 

 important case is that of the equalization of temperatures 

 which is constantly taking place by the flow of heat from 

 hotter to colder bodies, or from hotter to colder parts of 

 the same body. The amount of heat received by the 

 cold body is equal to that lost by the hot body, but 



