December 13, 1895.] 



SCIENCE. 



809 



of direction is manifest in tlie unconscious ten- 

 dency to curve to tlie right or left in wallving 

 when blindfolded. My experiments with forty- 

 nine young men show {Nature XXXII. , 293 ; 

 Science XV., 14) that this divergence from a 

 right line is not owing to differences in the 

 length, or strength, or dexterity of the legs, 

 the physical factors that suggest a convenient 

 explanation of the phenomena, but to a lack of 

 coordination in the muscles of the legs, arising 

 from the defective supervision of their move- 

 ments by the senses. 



The ability to wallt in a given direction and 

 the proper interpretation of the inverted image 

 on the retina are alike determined by the 

 activities of the brain, including the central 

 sense organs, and physical considerations re- 

 lating solely to the peripheral organs concerned, 

 which take into the account but a single factor 

 in a complex problem, cannot be accepted as 

 furnishing satisfactory explanations of physio- 

 logical processes. Manly Miles. 



Lansing, Mich., November 27. 



SCIENTIFIC LITERATURE. 

 Elements of the Mathematical Theory of Electricity 

 and Magnetism. By J. J. Thomson. Cam- 

 bridge University Press. New York, Mac- 

 millan,& Co. 1895. Crown 8°. Pp. vi. 

 510. 

 Electricity and Magnetism. A Mathematical Treat- 

 ise for Advanced Undergraduate Students. By 

 Francis A. Nipher. St. Louis, John L. 

 Boland Book and Stationery Co. 1895. 

 Crown 8°. Pp. xi. 426. 



Prof. J. J. Thomson is well known as the 

 worthy successor to the chair of Maxwell and 

 Lord Rayleigh. He has been hitherto known 

 chiefly for his work in mathematical physics, 

 and latterly for his numerous experimental re- 

 searches. This book exhibits him in a new 

 light, namely, as a teacher of elementary stu- 

 dents, and plainly declares him a master in that 

 domain. The subject of ' Electricity and Mag- 

 netism ' is one that lends itself readily to appli- 

 cations of many of the most difficult portions of 

 analysis, and it is generally supposed that an 

 exact comprehension of the various essential 

 parts of the theory is .only to be attained by 

 those persons who possess a thorough mathe- 



matical training. Maxwell's great work is a 

 bugbear to many a student on account of the 

 mathematical difficvilties which it undoubtedly 

 contains. How mistaken the idea is that the 

 essentials of the theory cannot be presented to 

 a person of but slight mathematical training, 

 a perusal of this delightful book will show. 

 The reviewer often recalls the words of one of 

 his old professors in college, who was wont to 

 ask the student who had successfully deduced 

 some differential equation to ' translate that 

 into English.' Prof. Thomson's book consists 

 in doing exactly this for the whole theory of 

 Electricity and Magnetism. In this respect it 

 marks almost a new departure in text-books, 

 for while we are familiar with books which, by 

 leaving out difficulties, and by the use of the 

 process known in England as ' Calculus-dodg- 

 ing,' attempt to attain simplicity, we have never 

 before come across a treatment at the same time 

 so full, so clear and exact, of this particular 

 subject. There are, to be sure, two examples 

 of this style of book. If one were asked to 

 name the best English treatise on Thermody- 

 namics he would still have to answer, Max- 

 well's 'Theory of Heat.' ' And yet Maxwell's 

 ' Heat ' contains very few mathematical symbols. 

 Still if one thoroughly understands the essential 

 principles contained in the book, and has a 

 thorough knowledge of mathematics, he will 

 be well able to write the mathematical treat- 

 ment for himself. A second example is Max- 

 well's 'Elementary Treatise on Electricity,' of 

 which we are at once reminded by the present 

 work. Maxwell, however, there treated but a 

 small portion of the subject, principally electro- 

 statics. What Maxwell would have written 

 had he lived to the present day, and treated of 

 Magnetism and the Electromagnetic Field in 

 general, would have probably resembled what 

 Prof. Thomson has given us. This is perhaps 

 a sufficient compliment, but we are tempted to 

 use the trite illustration of the ' flower from the 

 crannied wall,' and say that if one fully compre- 

 hended the ' all in all ' of this book, he would 

 be possessed of what is worth knowing of the 

 modern theory of electricity, and with the help 

 of a sufficient knowledge of Green's Theorem 

 and the properties of definite integrals he could 

 spin it out into two thick volumes of mathe- 



