July 26, 1901.] 



SCIENCE, 



147 



clearly stated on page 206, where is ascribed, 

 to him the first explicit record of a change in 

 the variation (declination). "While Columbus," 

 writes the author, "may not hence be said to 

 have discovered the variation, he must be 

 credited with having been the first to make it 

 known, as well as the first to discover a line of 

 no-variation." The author might have added 

 that this agonic line lay a little to the west of 

 the island of Fayal, one of the Azores ; and 

 he might also have informed the reader that 

 the variation of the compass was not generally 

 accepted as a fact until the middle of the six- 

 teenth century — Gilbert's time — being supposed 

 to be due to the mechanical defects of the com- 

 pass itself. 



The explanation of the earth-couple acting 

 on the compass needle, given on page 383, is 

 rather involved. The matter would be greatly 

 simplified by discussing the usual expression, 

 viz., Hml sin ^ deduced from a diagram on page 

 295. We notice that the author here resolves 

 H at right angles to the length of the magnet, 

 still the force acting at each end of the needle 

 parallel to the magnetic meridian is not H but 

 Hm ; and the arm of the couple is I sin 6 so that 

 the twisting moment is Hml sin 0. 



It is necessary, when studying the distribu- 

 tion of free magnetism in a bar magnet, by the 

 method given on page 181, to point out that the 

 bar must be so placed that the axis of the com- 

 pass-needle when at rest will lie in the magnetic 

 meridian, with its north-seeking pole pointing 

 magnetic north. 



We are told on page 152 that a small magne- 

 tized bar will place itself equatorially when sus- 

 pended between the poles of a horse-shoe mag- 

 net of nearly equal strength. This surely is a 

 lapsus calami, for the bar will set, not equatori- 

 ally, but axially. 



A very important feature of this treatise is to 

 be found in the diagrams and illustrations dis- 

 tributed throughout every one of its twelve 

 chapters. Many of them are original, and are 

 excellent efforts at representing graphically 

 some difficult points in what we may term the 

 physics of the ether. Teachers and students 

 alike will find them very useful. 



The author's object in the first part of his 

 treatise is to give such information about the 



principal phenomena of magnetism and corre- 

 lated subjects as will prepare the way for an 

 intelligent grasp of the matter to be discussed 

 in the second volume ; and in this he has w'ell 

 succeeded. The work is full of up-to-date in- 

 formation set forth in a clear and frequently im- 

 pressive manner. It makes one eager for the 

 appearance of the concluding volume, which 

 will treat of such practical matters as the com- 

 pass, the ship considered as a magnet, swinging 

 the ship, compensation of the deviations and 

 the mathematical theory of these deviations. 



Part I. extends to 556 pages and contains 

 368 figures, the whole put forth in the pub- 

 lisher's well-known excellent style. 



M. F. O'Eeilly. 



Animal Life : a First Book of Zoology. By David -^ 



Starr Jordan and Vernon L. Kellogg. 



New York, D. Appleton & Co. 12mo. Pp. 



329 ; frontispiece and 180 plates and figures 



in the text. Cloth, $1.20. 



This handy, beautifully printed and illus- 

 trated book is a distinct attempt to introduce 

 to the reader the subject of zoology from the 

 standpoint of the life of the animal rather than 

 from the purely systematic or comparative 

 anatomy side. It is a book to read and enjoj'' 

 in the fields and woods or at home rather than 

 a manual to study in the laboratory. Its scope 

 is w^ell stated in the general headings of its 

 sixteen chapters : (I.) The Life of the Simplest 

 Animals ; (II.) The Life of the Slightly Com- 

 plex Animals ; (III.) The Multiplication of 

 Animals and Sex ; (IV.) Function and Struc- 

 ture ; (V.) The Life Cycle ; (VL) The Primary 

 Conditions of Animal Life ; (VII.) The Crowd 

 of Animals and the Struggle for Existence ; 

 (VIII.) Adaptations ; (IX.) Animal Communi- 

 ties and Social Life ; (X.) Commensalism and 

 Symbiosis ; (XL) Parasitism and Degeneration ; 

 (XII.) Protective Resemblances and Mimicry ; 

 (XIII.) The Special Senses ; (XIV.) Instinct 

 and Reason ; (XV.) Homes and Domestic 

 Habits; (XVI.) Geographical Distribution of 

 Animals. Following the text proper are a 

 table of the systematic position of the animals 

 mentioned, a glossary and finally an excellent 

 index. 



In the subject matter of the volume one can- 



