[From Nature, Vol. vin.] 



LVIII. An Fumy on the M<itJ,<-ntntical Principles of Physics, &c. By the Rev. 

 James Challis, M.A., F.R.S., F.R.A.S., Plumian Professor of Astronomy and 

 Experimental Philosophy in the University of Cambridge, and Fellow of 

 Trinity College. (Cambridge: Deighton, Bell, and Co., 1873.) 



THIS Essay is a sort of abstract or general account of the mathemn 

 and physical researches on which the author has been so long engaged, portions 

 <>f which have appeared from time to time in the Philosophical Magazine, ami 

 also in his larger work on the " Principles of Mathematics and Physics." I ; 

 is always desirable that mathematical results should be expressed in intelligible 

 language, as well as in the symbolic form in which they were at first obtained. 

 and we have to thank Professor Challis for this Essay, which though, or rather 

 liecause, it hardly contains a single equation, sets forth his system more clearly 

 than has been done in some of his previous mathematical papers. 



The aim of this Essay, and of the author's long-continued labours, i 

 advance the theoretical study of Physics. He regards the material universe as 

 "a vast and wonderful mechanism, of which not the least wonderful qualit-. 

 its being so constructed that we can understand it." The Book of Nature, in 

 fact, contains elementary chapters, and, to those who know where to look for 

 them, the mastery of one chapter is a preparation for the study of the next. 

 The discovery of the calculation necessary to determine the acceleration <>f a 

 particle whose position is given in terms of the time led to the Newtonian 

 epoch of Natural Philosophy. The study from the cultivation of which our 

 author looks for the " inauguration of a new scientific epoch," is that of tin- 

 motion of fluids, commonly called Hydrodynamics. The scientific method \\hic-h 

 he recommends is that described by Newton as the "foundation of all philo- 

 sophy," namely, that the properties which we attribute to the least parts t 



