112 



SCIENCE. 



[N. s. Vol. XVIII. No. 447. 



vertex involve the solution of a right- 

 angled triangle for two of its parts. 



Since it seems to be almost certain that 

 a proposed great circle track will in reality 

 be sailed as a series of rhumb lines each 

 terminating in or near the great circle, the 

 methods of Mercator sailing will still be 

 found useful. By aid of a set of merid- 

 ional scales, problems in Mercator sailing 

 can be worked with great facility. For, 

 the board, the imiformly divided scales, 

 and the T-square constitute an ordinary 

 traverse table, and the departure is readily 

 converted into difference of longitude 

 through the equation 



„.™ , merid. diff. lat. ^^ , , 



D ff. long. = -— T .„ , ^ ^ X departure. 



•^ true diff. lat. 



To do this, suppose the meridional differ- 

 ence of latitude to be laid off upon a uni- 

 form scale rotating aboiit the pin or pivot. 

 Let the true difference be laid off along, or 

 parallel to, the initial line. Rotate the 

 former scale until the T-square indicates 

 that the point representing meridional dif- 

 ference is directly above that representing 

 true difference. Now slide the T-square 

 along until a point in the initial line is 

 reached which denotes the value of the de- 

 parture. The reading of the rotated scale 

 directly above this point is the difference of 

 longitude. 



In conclusion, it should be said that the 

 aim has been to use the drawing board 

 proper merely as a surface upon which to 

 locate points or lines temporarily, the ac- 

 curacy of the work depending upon the fact 

 that the scales and border of the board are 

 not sub.jeet to any considerable atmospheric 

 or temperature changes. R. A. Harris. 



SCIENTIFIC BOOKS. 

 Zoology: Descriptive and Practical. By Buel 

 P. CoLTON, A.M. Boston, D. C. Heath & 

 Co. 1903. Part I., Descriptive, pp. s + 

 375. Part II., Practical, pp. xvii -f 204. 

 Cotton's 'Practical Zoology,' which was pub- 



lished seventeen j^ears ago, did excellent pio- 

 neer work as a laboratory guide for secondary 

 schools. This useful liaud-book, revised and 

 amplified, now appears in connection with an 

 excellent descriptive zoology. 



In the latter the author introduces each of 

 the larger groups of animals by a description 

 of a typical example, treating of its morpho- 

 logical and physiological characteristics and 

 paying especial attention to its habitat, move- 

 ments, senses, capture of prey, taking of food 

 and manner of self defense. 



Natui-ally, Arthropods, and particularly In- 

 sects, have a prominent place at the begin- 

 ning, followed by a brief account of the An- 

 nulata, a somewhat longer description of the 

 Mollusca and an extended discussion of the 

 Chordata. Thereupon the Protozoa, Porifera, 

 Coelenterata, Echinodermata, Platyhehninthes, 

 Trochelminthes and Molluscoidea are taken 

 up in the order given. This is an excellent 

 practical arrangement on the whole, though it 

 might have been still better to have placed the 

 Annulata and Echinodermata last and thus 

 have preserved the ascending order through- 

 out each of the two sections, for the sake of 

 avoiding those misconceptions which are wont 

 to arise in the mind of the beginner, to whom 

 position in a test-book has a profound signifi- 

 cance. 



The strongest feature of the book is its 

 broad treatment of animal life, in other words, 

 its natural history. The author has a keen 

 sense of what is interesting. His style is 

 simple and direct, and the book is thoroughly 

 readable. 



The author did not cease to do pioneer work 

 when he published his 'Practical Zoology' 

 seventeen years ago. In the present book he 

 makes free use of ' tho,' 'thru,' 'thoro' and 

 their various compounds, while ' celom,' ' ce- 

 cum,' ' hemal ' and a few other words have 

 been stripped of superfluous letters. He does 

 not attempt to set right names like Amoeba, 

 which are apparently protected by their Latin 

 form, but one is surprised that ' coelenterates,' 

 ' diaphragm ' and a few other terms should 

 not have been pruned. Spelling reform has 

 much in its favor, and it must be introduced 



