546 THE POPULAR SCIENCE MONTHLY. 



"Nor should we counsel a man to venture upon physical speculations who 

 converts the proposition ''heat is insensible motion'' into ' insensible motion is 

 heat,'' and hence concludes that when a force is applied to a mass so large that 

 no motion is seen to result from it, or when, as in the case of sound, motion 

 gets so dispersed that it becomes insensible, it turns to heat." 



Respecting the first of the two statements contained in this sen- 

 tence, I will observe that the reader, if not misled by the quotation- 

 marks into the supposition that I have made, in so many words, the 

 assertion that " insensible motion is heat," will at any rate infer that 

 this assertion is distinctly involved in the passage named. And he 

 will infer that the reviewer would never have charged me with such 

 an absurd belief, if there was before him evidence proving that I have 

 no such belief. What will the reader say, then, when he learns, not 

 simply that there is no such statement, and not simply that on the 

 page referred to, which I have ascertained to be the one intended, there 

 is no such implication visible, even to an expert (and I have put the 

 question to one), but when he further learns that, in other passages, 

 the fact that heat is the one only of modes of insensible motion is dis- 

 tinctly stated (see " First Principles," §§66, 68, 171), and when he 

 learns that elsewhere I have specified the several forms of insensible 

 motion ? If the reviewer, who looks so diligently for flaws as to search 

 an essay in a volume he is not reviewing to find one term of an incon- 

 gruity, had sought with equal diligence to learn what I thought about 

 insensible motion, he would have found in the " Classification of the 

 Sciences," Table II., that insensible motion is described by me as hav- 

 ing the forms of heat, light, electricity, magnetism. Even had there 

 been, in the place he names, an unquestionable implication of the belief 

 which he ascribes to me, fairness might have led him to regard it as 

 an oversight, when he found it at variance with statements I have 

 elsewhere made. What, then, is to be thought of him when, in the 

 place named, no such belief is manifest, either to an ordinary reader 

 or a specially-instructed reader ? 



No less significant is the state of mind betraved in the second 

 clause of the reviewer's sentence. By representing me as saying that, 

 when the motion constituting sound " gets so dispersed that it becomes 

 insensible, it turns to heat," does he intend to represent me as thinking 

 that, when sound-undulations become too weak to be audible, they be- 

 come heat-undulations ? If so, I reply that the passage he refers to 

 has no such meaning. Does he then allege that some part of the 

 force diffused in sound-waves is expended in generating electricity, 

 by the friction of heterogeneous substances (which, however, eventu- 

 ally lapses from this special form of molecular motion in that general 

 form constituting heat), and that I ought to have thus qualified my 

 statement ? If so, he would have had me commit a piece of scientific 

 pedantry hindering the argument. If he does not mean either of 

 these things, what does he mean ? Does he contest the truth of the 



