i873«] Notices of Books. 399 



The seventh lecture is devoted to a subject which Prof. 

 Helmholtz has largely contributed to establish and develop — 

 the Conservation of Force. This law, which possesses a great 

 generality of application, although partially recognised by 

 Newton and Daniel Bernouilli, by Rumford, Davy, and others, 

 was first enunciated in its universality by Dr. Julius Mayer, in which 

 work he was ably supplemented by the admirable experimental 

 results obtained by our countryman Joule. The law asserts that 

 the " quantity of force which can be brought into action in the 

 whole of Nature is unchangeable, and can neither be increased 

 nor diminished." The law has been so admirably illustrated 

 and discussed by Tyndall and others in this country, that we need 

 scarcely allude to the details of this lecture. We may mention, 

 however, in passing, the fertility of illustration which the author 

 possesses ; among other experiments we notice (Fig. 47, p. 345) 

 a means of producing fire by the simple friction of two pieces of 

 wood after the manner of the savages, but which we have in vain 

 tried to do even by the use of a turning lathe and two pieces 

 of wood differing considerably in hardness. 



The eighth and last lecture, on " The Aim and Progress of 

 Physical Science," was delivered in Innsbruck in 1869. In 

 this the author enters into a discussion of various ideas which 

 have — some for a longer, some for a shorter time— been floating 

 about on the confines of recognised science. He pays an 

 elaborate tribute of admiration to the doctrines of Darwin, dis- 

 cusses various questions concerning life ; and is led to remark 

 that "the recent progress of physiology and medicine is pre- 

 eminently due to Germany." Yet he is fain to admit that "both 

 in England and France we find excellent investigators, who are 

 capable of working with thorough energy in the proper sense of 

 the scientific methods ; hitherto, however, they have almost 

 always had to bend to social or ecclesiastical prejudices, and 

 could only openly express their convictions at the expense of their 

 social influence and their usefulness." This was written ten 

 years ago. We hope Prof. Helmholtz knows how much these 

 things have changed in England even during that short period. 



Here, then, we end our notice of a book, which even in its 

 translated form possesses, quite irrespective of the actual science 

 which it contains, a certain charm of style and diction seldom met 

 with in works of this nature, most seldom to be met with at the 

 hands of exact and profound thinkers. We find here our ardent 

 investigator, our original thinker, our profound mathematician, 

 introducing into the most complex subjects a grace of culture 

 and an elegance of expression which it is always satisfactory to 

 meet with, and which indicates the man of great general as well 

 as special knowledge. We find constant quotations from the 

 philosophical poets of Germany ; Prof. Helmholtz evidently 

 adores " Faust," is evidently pervaded by a spirit as full of 

 harmony as any of those great sonatas of " the mightiest among 

 the heroes of harmony " Beethoven. 



