A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE. 



" To the solid ground 

 Of Nature trusts the mind which builds for aye." — Wordsworth. 



THURSDAY, MAY 4, 1893. 



AN AMERICAN TEXT-BOOK OF PHYSICS. 

 Physics, Advanced Course. By George F. Barker, Pro- 

 fessor of Physics in the University of Pennsylvania. 

 Pp. 902. (London: Macmillan and Co., 1892.) 



THE days are nearly over when a text-book of Physics 

 in one volume is any longer a possibility. The 

 attempt to compress so great a mass of knowledge into 

 small compass seems necessarily to involve the omission 

 of anything like the full elementary explanation re- 

 quired by junior students, as well as the more advanced 

 discussion suitable to seniors ; it also appears necessary 

 to curtail any approach to a mathematical investiga- 

 tion, and to dispense with the details of experimental 

 appliances. 



With so much omitted it may surprise those who do not 

 know what a vast region is now cultivated under the name 

 Physics, that there is enough left to fill a bulky volume. 

 But there is, and this volume contains it, viz. the quiet 

 and systematic rehearsal of the broad facts of the 

 subject, a statement free from rhetoric and from effort, 

 a statement which flows placidly on in a peaceful and 

 easy flow. 



The absence of friction renders the -book hardly 

 suitable for a beginner, especially one without a 

 teacher ; he could hardly manage to grip the facts as 

 they passed him. But after a serious course of lectures, 

 after a disjointed struggle with difficulties in this or that 

 department, it would be a pleasant relief to a student to 

 have a book like this put into his hands as a kind of 

 glorified note-book, that he may leisurely revise the 

 whole in a corrected and simple form. If a third year 

 student is able to read this book feeling that it con- 

 tinually excites in him recollections of the more detailed 

 treatment he has elsewhere acquired, he may be satis- 

 fied that he knows a good deal of Physics ; if, on the 

 other hand, he comes across pages where the matter is new 

 and where he has any diffieulty in apprehending what is 

 said, he may feel assured that here there is something 

 desirable for him to attend to and learn from any of the 

 more detailed and elaborate sources open to him. 

 NO. 1227, VOL. 48] 



That is how the book strikes me : as one eminently 

 suited to assist a student's revision of the subject, so as 

 to ensure that his knowledge may be free from glaring 

 gaps ; but not as a book that could be recommended for 

 learning from. It would probably, as I have said, be 

 difficult to learn from, but a still more fatal objection to 

 its use by a solitary learner is the probability that its easy 

 flow would convey an altogether erroneous impression of 

 the difficulties that really bristle about the subject, and 

 would lead to only a very superficial smattering, quite 

 incommensurate with the vast amount of information 

 which is summarised and made more or less palatable 

 by this genial treatise. 



Having thus indicated what seems to me the general 

 usefulness of the book I proceed to indicate its contents. 

 It begins with fundamental units and the laws of 

 mechanics, together with a summary of the properties of 

 matter. Then it proceeds to treat of Energy as belonging 

 to various bodies ; masses, molecules, and the ether. This 

 is the classification definitely adopted throughout the 

 book — it is a treatise on the forms of energy. " Mass 

 physics, molecule physics, and asther- physics; and the fact 

 is significant that to the last division of the subject it has 

 been found necessary to devote more than half of the 

 entire work." " Radiation is considered broadly, without 

 any special reference to those wave-frequencies which 

 excite vision and are ordinarily called light." Modern 

 references abound, and the subjects dwelt on are those 

 which at the present time are most exciting attention, 

 " The author's aim has been to avoid making the book 

 simply an encyclopaedic collection of facts on the one 

 hand, or too purely an abstract and theoretical discussion 

 of physical theories on the other." " He has made free 

 use of all the sources of information at his command. . . 

 The names of those physicists to whom the science is 

 most deeply indebted are given in connection with the 

 subjects on which they have worked, and in order to 

 bring the student into more intimate contact with these 

 great minds, the laws or principles they have formulated 

 have frequently been given in their own words." 



This free quotation is characteristic of the book, and 

 sometimes it could be wished that a chapter and verse 

 reference for further following up had been given, instead 

 of only the mere name. But, after all, such reference 



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