Notices respecting New Books. 369 



Lapps they introduced navigation by compass into Scandinavia. 

 The subsequent dissemination of the knowledge to various Euro- 

 pean ports took place through the medium of traders to the Baltic. 

 "Vixere fortes ante Gilbertum" if we may be pardoned for altering 

 Horace; the author has discovered at least two such philosophers, 

 JNTeckam and Peregrinus. We cannot agree with Dr. Benjamin 

 in his criticism of a statement by Peregrinus (p. 174), which he 

 considers erroneous. Concerning the rubbing of iron against lode- 

 stone or a magnet Peregrinus writes : " You will infer what part of 

 the iron is attracted to each part of the heavens from knowing 

 that the part of the iron which has touched the southern part of 

 the magnet is turned to the northern part of the sky. The con- 

 trary will happen with respect to that end of the iron which has 

 touched the north part of the stone, namely, it will direct itself 

 towards the south." For the thirteenth century this is surely a 

 very concise and straightforward description, contrasting greatly 

 with the author's confusion of true north polarity and north-seeking 

 magnetism. 



The volume contains several reproductions of interesting old 

 prints and good portraits of Gilbert, vou Guericke, and Franklin. 



J. L. H. 

 An Introductory Treatise on the Lunar Theory. By E. W. Browjnt, 



M.A., Professor of Applied Mathematics in Haverford College, 



Pa. (Cambridge University Press.) 

 It may be said, and indeed it has been remarked by foreign and 

 English writers alike, that the English student of mathematics is 

 exceedingly fortunate in the excellence and abundance of the 

 mathematical text-books at his disposal. It is therefore not a 

 little curious that the only elementary exposition of either the 

 Lunar or the Planetary Theory has existed in the form of a 

 single and, it must be admitted, very inadequate introductory 

 treatise. At the same time, the field for original research offered 

 •by these particular cases of the general problem of Three Bodies 

 has been, with notable exceptions, singularly neglected by English 

 mathematicians ; and it is at least doubtful if the contributions of 

 Lubbock, Airy, Cayley, and Adams are sufficient to relieve English 

 mathematics of the serious charge of having neglected an im- 

 portant branch of the science. Eor this state of things the want 

 of a good elementary and, at the same time, comprehensive treatise 

 was doubtless largely responsible, for there was apparently little 

 to attract the student to take up a subject in which it would be 

 necessary for him at an early stage to master the contents of a 

 great number of scattered and exceptionally obscure original 

 memoirs. It is therefore with reason that we extend a special 

 welcome to Prof. Brown's treatise. The author, who, although 

 holding an appointment abroad, was formerly Fellow of Christ's 

 College, Cambridge, is already favourably known both on account 

 of his own contributions to the most modern form of the Lunar 

 Theory and also for his elucidation of the work of the older 

 theorists. 



The work divides itself practically into two distinct parts, the 

 Phil. Mag. S. 5. Vol. 42. No. 257. Oct. 1896. 2 D 



