Notices respecting New Books. 335 



La CTialeur (Heat). By Pieere de Heex, Professor of Experi- 

 mental Physics in the University of Liege. Liege : Nierstrasz, 

 1894. 



Ix the somewhat remarkable preface to this work the author 

 discusses the two methods of studying science by mere experiment 

 and deduction therefrom, and by assumption of a theory which is 

 afterwards put to the test of crucial experiment, respectively. It 

 is ouly by the latter method that we succeed in acquiring a know- 

 ledge of the causes of things, which is the true aim of physical 

 science. In the ordinary text-books of heat (and indeed of all 

 branches of physics, except perhaps sound) the former method 

 has been generally adopted ; a miscellaneous collection of facts is 

 given concerning expansion, the laws of gases, calorimetry, &c, 

 and these lead to a higher analytical or mechanical development of 

 the subject, but no theory is given to unite them into a connected 

 system. Such a connecting link is first met with in the kinetic or 

 molecular theory of gases, by which the behaviour of gases under 

 various conditions of temperature and pressure is completely 

 explained. By a suitable choice of temperature and pressure, 

 however, a gas may be changed to liquid, or a liquid to solid, so 

 that a similar theory must apply to all three states of matter. 

 But as the molecules become crowded together the increasing 

 complexity of their motions defies all calculation, although Yan 

 der Waals and others of the same school, to whose influence the 

 present w r ork is doubtless due, have achieved a certain amount of 

 success in the case of liquids near their critical temperatures. 

 Again, if we grant that the properties of liquids and solids are 

 capable of explanation by molecular motion, it follows that such 

 properties will be functions of the molecular weights of the 

 substances. This conclusion has been verified in many cases in 

 which a complete explanation is yet wanting. 



In the volume before us heat is regarded as a molecular motion, 

 and its chief phenomena are explained from this point of view as 

 far as is possible in the present state of knowledge. The author 

 assumes a knowledge of elementary phenomena, and occasionally 

 borrows formulas from thermodynamics, so that his work must be 

 considered as an exposition of molecular physics rather than a 

 text-book of heat. We have found several misprints in the book, 

 notably in connexion with names of authors, for example Claira//t. 

 Peluj, Quinke, all of which might be corrected in a future edition. 



James L. Howard, 



