238 



SCIENCE. 



counter to certain authors whom they are disposed to 

 consider as authorities. But, in my view of the case, 

 Science has no authority, except the authority of facts, 

 and theoretical views are always fair food for criticism. 

 Mr. Dolbear quotes from Clausius to the effect that "all 

 heat existing in a body is appreciable by the touch or the 

 thermometer; the heat which disappears * * * * 

 exists no longer as heat, but has been converted into 

 work." Heat is undoubtedly appreciable, but not neces- 

 sarily measurable, by the touch or the thermometer. As 

 the heat capacity of any substance increases its tempera- 

 ture effect for equal volumes of inflowing heat dimin- 

 ishes, so that the thermometer fails to indicate the exact 

 quantity of heat which a substance receives in passing 

 through a fixed range of temperature. It is customary 

 in late authors to speak of this apparently lost heat as 

 converted into work, or, in other cases, to speak ot it as 

 changed from actual into potential energy. This is, un- 

 doubtedly, a very convenient way of getting around the 

 difficulty; but, with all due deference to the distinguished 

 writers who advance this hypothesis, I venture to ques- 

 tion if it is a strictly scientific way. To come plump up 

 against a difficulty in your path, to explain this difficulty 

 by a nicely sounding word which explains nothing, and 

 then to go swimmingly on, enables one to get over a 

 great deal of ground in a short time ; but it is very apt 

 to leave stumbling blocks tor those who come after. 



I should certainly like to see a precise definition of the 

 word "work" in this connection. Htat produces a cer- 

 tain effect. That effect is calltd work. But the impor- 

 tant question remains, what has become of the heat ? It 

 was a motion. Has it ceased to be a motion ? If so, 

 then motion can cease to exist. Yet I hardly think any 

 scientist will admit such a possibility. But if it has not 

 ceased to be motion, where is it ? Is the word " work " 

 advanced as a name lor some new mode of motion ? 

 Whether it is or not, however, it fails to explain what 

 has become of the heat. We meet with a like difficulty 

 in the theory of the conversion of actual into potential 

 energy. Actual energy we can readily comprehend ; it is 

 the energy of the motion of masses. But what is poten- 

 tial energy ? It is a possibility of mass motion. A body 

 rests upon the earth. It cannot possibly descend further. 

 It has no potential energy. A body is suspended in the 

 air. It may possibly descend further. It has potential 

 energy. Potential energy then, is possibility of motion. 

 Actual motion has been converted into possible motion. 

 If this amounts to more than the explaining of a difficulty 

 by a meaningless phrase, I should certainly be glad to 

 have some one scientifically explain the explanation. I 

 must quote from my former article : " Motion is motion 

 and cannot possibly be or become anything else." Ac- 

 tual motive energy cannot cease to exist, and be replaced 

 by an abstract possibility of motion, called potential 

 energy. 



In regard to Mr. Rachel's remarks on my views re- 

 specting variation in heat capacity, he must permit me to 

 correct his quotation. He quotes me as saying : " Tem- 

 perature and heat are very different things." I find my 

 expression to be : " Temperature and absolute heat are 

 very different things." There is a considerable difference 

 of meaning between these two expressions, which it 

 would have been well for him to give me credit for. The 

 main difficulty in the minds of both my critics seems to 

 be a somewhat contused idea as to whit constitutes heat. 

 Mr. Dolbear claims that the free vibration of molecules is 

 not heat. In this he certainly disagrees with most auth- 

 ors. Mr. Rachel states that " latent heat is not heat." 

 He intimates that it is wotk, but will he be kind enough 

 to explain scientifically just what work means in this 

 connection ? He says further, " Water does not con- 

 tain more heat than ice at 32° ; it contains * * * more 

 motion, but not motion of the heat kind." Of what kind 

 then ? "Nor is it true that as density diminishes the heat 



capacity increases." The heat has disappeared as heat, 

 ",but it nevertheless exists in the gas as a greater range 

 of mobility." 



We here get his definition of " work." It is " motion, 

 but not motion of the heat kind ; " it is " a greater range 

 of mobility." Motion, then has not ceased to exist, and 

 we have been splitting hairs about nothing. It is mole- 

 cular motion, but not the special mode of motion which 

 he calls heat. Yet it would be well to bear in mind that 

 scientists are somewhat indefinite in their ideas as to just 

 what mode of motion does constitute heat. In one case 

 they speak of radiant waves as heat, in another as local 

 molecular vibrations as heat ; in a third, ot the free mo- 

 tions of gas particles as heat, and in a fourth, of motive 

 influences which cease to affect the thermometer as heat, 

 for what else is meant by absolute heat ? The authori- 

 ties certainly consider that heat continues to exist as 

 heat in the case of increased heat capacity, when they 

 assert that specific heat varies with variation in the 

 temperature of substances. Thus it seems that all mo- 

 tive influences of which we become aware in matter, 

 outside of gravity, electricity, magnetism, light, chem- 

 ism, and mass motion, are grouped together as heat, 

 their varying conditions being simply pointed out by 

 qualifying adjectives. The phrase, " Latent Heat," has 

 by no means gone out of use. Sir William Thomson, 

 in the last edition of the Encyclopedia Britannica, con- 

 siders it necessary to still retain it. In fact there are 

 various modes ot motion, some centrifugal, others centri- 

 petal in their effects, so closely related to ordinary heat, 

 that it has proved more convenient to consider them as 

 special heat conditions than to devise separate names for 

 them. 



Mr. Rachel is still more decisive in regard'to another 

 portion of my article. He says, " Mr. Morris's concep- 

 tion of the action of gravity is still more erroneous. 

 This gentleman says, 'the eaith must fall towards the 

 body with the same energy that the body displays in fall- 

 ing towards the earth ' ! Now the two fundamental laws 

 of gravitation, as discovered by Newton, are attraction 

 acts in direct proportion to mass and in indirect propor- 

 tion to square of distance. The statement of Mr. 

 Morris is therefore absolutely false." 



Perhaps so, yet I hardly think that Newton himself 

 would have so absolutely denied my proposition. Let 

 us suppose the falling body to be increased until it equals 

 the earth in weight. What would follow then — would 

 not gravity cause them to approach each other with 

 equal energy? Their attractive pulls upon each other 

 would be equal, and therefore the effects of these pulls 

 must be equal. 



If, however, the falling body be greatly decreased in 

 weight, this may seem to some to changethe elements of 

 the problem. Yet it can readily be shown that difference 

 in weight makes no difference whatever in the result. 

 We must not look upon the earth as fixed and the fall- 

 ing body alone as movable. They are both freely float- 

 ing masses, each capable of yielding to any exterior im- 

 pulse. The size or weight has nothing to do with the 

 question. If an atom and the earth be side by side, and 

 beatttacted by a distant mass with the same vigor, they 

 must move with equal energy towards it. Yet an energy 

 which would give the atom excessive speed would pro- 

 duce an inappreciable effect upon the earth. 



Suppose, for the sake of illustration, that the falling 

 body weighs one pound and the earth one million pounds. 

 Then the falling body will attract each pound of the 

 earth's 'mass with a vigor dependent on its distance, and 

 be attracted by it with equal vigor. To reach the whole 

 attraction of the falling body we must add together this 

 million of separate attractions. But, in like manner, to 

 get the whole attraction of the earth we must add to- 

 gether its million of separate attractions. The body 

 exerts a separate attraction upon each pound of the 



