June 26, 1884] 



NA TURE 



191 



PROFESSOR TATT'S "MEAT" 

 Heat. By P. G. Tait, M.A., Professor of Natural Philo- 

 sophy in the University of Edinburgh. (London : 

 Macmillan and Co., 1SS4.) 

 A TREATISE on heat by one so eminent, both as 

 •'"*- physicist and teacher of Physics, needs no apology, 

 and yet no doubt the author is right in stating that his 

 work is adapted to the lecture-room rather than to the 

 study or the laboratory. Freshness and vigour of treat- 

 ment are its characteristics, and the intelligent student 

 who reads it conscientiously will rise from it not merely 

 with a knowledge of heat but of a good many other 

 things besides. 



" If science," says our author (p. 368), " were all re- 

 duced to a matter of certainty, it could be embodied in 

 one gigantic encyclopaedia, and too many of its parts 

 would then have . . . little more than the comparatively- 

 tranquil or, rather, languid interest which we feel in look- 

 ing up in a good gazetteer such places as Bangkok, Ak- 

 Hissar, or Tortuga." Not a few text-books of science are 

 precisely of the nature of such a guide without its com- 

 pleteness, and while they carry the student successfully to 

 the end of his journey, the way before him is made so 

 utterly deficient in human interest that he reaches his 

 goal with a sigh of relief, and looks back upon his journey 

 with anything but satisfaction — as a task accomplished 

 rather than as a holiday enjoyed. Now the presence of such 

 a human interest is the great charm of the work before us- 

 It may be a fancy on our part, but we cannot help liken- 

 ing our author to the well-known guide of Christiana and 

 her family. Both have been equally successful in the 

 slaughter of those giants whom the older generation of 

 pilgrims had to find out for themselves and encounter 

 alone. But here the likeness ends, for it is quite certain 

 that those who place themselves under the scientific 

 guidance of our author will not be treated like women or 

 children, but they will be taught to fight like men. And 

 surely to combat error is an essential part-of the educa- 

 tion of the true man of science, for, if not trained up as a 

 good soldier of the truth to defend the king's highway, he 

 will be only too apt to turn freebooter, and gain his live- 

 lihood by preying on the possessions of others. 



The first chapter contains the fundamental principles. 

 " Heat," says our author, " whatever it may be, is SOME- 

 THING which can be transferred from one portion of 

 matter to another ; the consideration of temperatures is 

 virtually that of the mere conditions which determine 

 whether or not there shall be a transfer of heat, and in 

 what direction the transfer is to take place." 



Then follows a preliminary historical sketch of the 

 subject, the result of which is that heat is now proved to 

 be a form of energy. Again : " The mechanism upon 

 which heat-energy depends is (probably at least) approxi- 

 mately known so far as regards heat in a gas and as 

 regards radiant heat. Beyond these we have, as yet; 

 little information on the subject." 



The following is a digression by the way : — 



" There can be no question about the fact that the 

 metre is inconveniently long, and the kilogramme incon- 

 veniently massive, for the ordinary affairs of life. The 

 average length of the arms of shop-girls, and the average 

 quantity of tea or sugar wanted at a time by a small 

 purchaser, have no conceivable necessary relation to the 



ten-millionth part of the quadrant of the earth's meridian 

 passing through Paris, or the maximum density of water. 

 But the standard yard and pound were, no doubt, origin- 

 ally devised to suit these very requirements as regards 

 the average dimensions of the shop-girl or the paying 

 powers of the ordinary customer. Yet this invaluable 

 superiority of our units over those of the metrical system 

 is, with an almost over- refinement of barbarism, thrown 

 away at once when we come to multiples or sub- 

 multiples.'' 



It may be desirable to quote the author's own words 

 regarding his classification of different kinds of heat : — 



" In the first place, we have absolutely no proof that 

 radiation from the sun is in any of the forms of energy 

 which we call heat while it is passing through inter- 

 planetary space. That it is a form of energy, and that it 

 depends upon some species of vibration of a medium, we 

 have absolute proof. But it seems probable that we are 

 no more entitled to call it heat than to call an electric 

 current heat ; for, though an electric current is a possible 

 transformation of heat-energy, and can again be frittered 

 down into heat, it is not usually looked upon as being 

 itself heat. Just so the energy of vibrational radiation is 

 a transformation of the heat of a hot body, and can again 

 be frittered down into heat — but in the interval of its 

 passage through space devoid of tangible matter, or even 

 when passing (unabsorbed) through tangible matter, it is 

 not necessarily heat." 



That this is not a mere question o! words may be seen 

 from the following considerations. According to Vr iory. 

 all kinds of radiant heat, whether these have issued from 

 a source of high or from one of low temperature, are in 

 presence of an absolutely black surface at once and 

 entirely converted into absorbed heat. On the other 

 hand, absorbed heat is only entirely converted into radiant 

 heat when the body from which it issues has been cooled 

 down to the absolute zero of temperature, a condition 

 which is practically unapproachable. 



The following are the subjects which appear to us to be 

 treated in the most original manner : — Thermo-electricity, 

 combination and dissociation, conduction, convection, and 

 radiation, discussion of isothermals and adiabatic lines- 

 In the development of thermo-electricity and of conduc- 

 tion the author has taken a. prominent part, and probably 

 we must blame the late mild winter for our not hearing 

 more about his latest research regarding the effect of 

 pressure upon the point of the maximum density of water. 



We cannot do justice to such a book in the course of a 

 short notice like the present ; we will therefore content 

 ourselves with a few quotations and remarks. The fol- 

 lowing (p. 72) is an excellently clear definition of an 

 isotropic body : — 



" An isotropic body is one from which, if a small sphere 

 were cut, it would be impossible to tell by any operation 

 on it how it originally lay in the solid — it has, in fact, pre- 

 cisely the same properties in all directions." 



In p. 91 an increase in clearness is produced by giving 

 the coefficient of dilatation of mercury at various tempera- 

 tures under three different heads, namely, mean coefficient 

 of dilatation from o°, coefficient referred to volume at 0°, 

 true coefficient. The following statement will be found 

 useful to meteorologists : — 



"Vertical (convection) currents at definite places may 

 be at once produced either by heating the requisite part 

 of the lower portions of a fluid mass, or by coolir.g that of 

 the upper portions. But the effects of cooling part of the 

 lower portions, or heating some of the upper, are usually 



