-446 Notices respecting New Boohs. 



preceding chapters. Successive chapters are devoted to such 

 subjects as congruent transformations, higher line-geometry, conic 

 sections, quadrics, &c, the principle of duality playing a most 

 important role throughout. The theory of curvature and torsion 

 of curves is developed in Chapter XV. ; and in Chapter XVI. 

 on differential line geometry the author includes some of his own 

 researches in isotropic congruences. The book is eminently 

 readable, and finishes with a picturesque comparison of the merits 

 of the three methods of approach. We are told that " there is no 

 answer to the question which method of approach is the best. 

 The determining choice among the three will, in the end, be a 

 matter of personal Aesthetic preference. And this is well. Let us 

 not forget that, in large measure, we study pure mathematics to 

 satisfy an aesthetic need. We are fortunate when, as in the present 

 case, we are free at the outset to choose our line of approach." 

 We have noticed two or three unimportant slips, such as 

 that in Theorem 32, p. 22, where some words are evidently 

 omitted. 



LehrbucJi der PractiscJien Fhysik. Dr. Fbiedkich Ivohleausch. 

 Eleventh edition. (Leipzig and Berlin, B. Gr. Teubner, 1910.) 

 M. 11. 



While this book is under review comes the news of the death 

 of its renowned author. In its present form it contains, therefore, 

 the last additions to be made by his own hand. It is a monu- 

 ment to a seeker after precision in physical measurement ; and, 

 especially in its latest form, it will serve to perpetuate the aims of 

 its author. The additions made in this eleventh edition are very 

 considerable. 



Important modifications have been made in many sections. 

 Eor example in connexion with recent work on absolute thermal 

 radiation and its practical applications, with the phenomena of the 

 cathode stream and the measurement of the ratio of charge to 

 mass ; with the phenomena of electric waves. But the most 

 important is an extra section of thiiiw-three pages in radioactivity. 

 This is the best summary we have yet seen of this subject from 

 the point of view of physical measurements and it should be of 

 immense service to the large number of new recuits who are con- 

 tinually being brought to this branch of study. Useful changes 

 have also been made in the tables at the end so as to bring them 

 completely up to date. There is no need to recommend the book 

 for it has already taken up an established position as a book of 

 reference in every physical laboratory. 



