436 



NATURE 



\Sept. 8. 1887 



the most readable of modern books of travel. The work 

 is divided into three parts, the first treating of the petrels, 

 the second of the frigate-birds, gannets, and tropic birds, 

 and the third of the gulls and terns. Mr. Green has given 

 a very correct account of all the best-known species 

 belonging to these groups, and for a second edition he 

 may find a few useful notes on some of his marine friends 

 in the volume published by the Royal Society on the 

 Transit of Venus Expedition to Kerguelen Island. One 

 at least of the notes here published is given by Mr. Green, 

 but only as an extract from our volume of " Aves " in 

 " Cassell's Natural History." The illustrations which 

 accompany the work may be sufficient to identify the 

 various species represented, especially the albatrosses, 

 but they are rather roughly done, and that of the flying 

 petrel is nothing but a caricature. No figures taken from 

 mounted birds are ever satisfactory, and Miss Green's 

 illustrations are no exception to the rule. 



Mr. Arnold's little work will rank with any that we 

 know of for pleasant reading, either from a sportsman's 

 or an ornithologist's point of view. Some of the descrip- 

 tions of game and wild-fowl shooting are exceptionally 

 good, and carry with them a scent of the moor and the 

 sea. Despite an acquaintance with several standard 

 works on birds, the author seems to cling with respect to 

 some of the more pretentious but second-rate books which 

 pass muster as histories of British birds. It is, however, 

 somewhat of a treat to find His Royal and Serene High- 

 ness the Prince of Mantua and Montferrat (!) spoken of 

 under his original title of Groom Napier, though we should 

 never call him a " first-class " authority. Many well- 

 known names are wrongly spelt throughout the book, and 

 these shortcomings should be corrected in a subsequent 

 edition, when we should also like to see that Seebohm's 

 excellent "History of British Birds" has come under the 

 author's ken. It is to works on natural history like Mr. 

 Arnold's, where real instruction is conveyed in elegant 

 English, so that the acquisition of knowledge is rendered 

 pleasant and easy, that we owe so much of the interest 

 which has of late years been awakened in scientific pur- 

 suits ; and we should be captious indeed were we to point 

 out small errors in a book the perusal of which has given 

 us so much enjoyment. Not the least useful feature of 

 the work is a chapter by Mr. Brodie Innes on " Grouse 

 Moors and Deer-Forests." 



Should the works under review pass into a second 

 edition, we should be glad to point out to the authors 

 certain emendations which have occurred to us, of too 

 little moment, perhaps, to mention in a review, but which 

 would add somewhat to the finish of the volumes. 



R. BOWDLER SHARPE. 



OUR BOOK SHELF. 



First Lessons in Science; designed for the use of Children. 

 By the Right Rev. J. W. Colenso, D.D. (London: 

 Ridgway, 1887.) 



This book was written more than a quarter of a century 

 ago for the use of a class of natives of the diocese of 

 Natal, who were learning to read English. Since then 

 the greater part of it has been rewritten in order to adapt 

 it to the necessities of European children. As far as 

 possible the earlier lessons are written in words of one 



syllable, so that they are well fitted for the use of those 

 for whom they are intended. 



The object of the work is to furnish the readers with 

 useful information concerning the things around them, in 

 place of the usual childish stories contained in the first 

 books of English ; at the same time presenting only such 

 facts as ought, according to the good Bishop, and we 

 quite agree with him, to be known by everyone. We 

 venture to think that in this respect the native students 

 under Bishop Colenso's care were much better off, having 

 these lessons in their possession, than the boys and girls 

 of our own schools who were learning English at the 

 same time. 



By far the greater part of the book is devoted to 

 astronomy, to which subject it forms really an admirable 

 introduction. This of course necessitates the introduc- 

 tion and explanation of many geometrical and optical 

 terms, all of which are put forth in the best possible way. 

 The physical features, and orbital and apparent motions 

 of all the members of our system, including comets and 

 meteorites, are fully considered, as are also the apparent 

 motions of the stars. 



The reasons are also given why the observed place of 

 a heavenly body should be corrected for refraction, paral- 

 lax, aberration, precession, and nutation. Kepler's laws 

 and the law of gravitation also come in for a fair share of 

 attention. 



Some of the figures should be brought up to date. We 

 are told that the earth is 96,000,000 miles from the sun, 

 and that between forty and fifty minor planets are known ; 

 whereas the distance of the sun is between 92.000,000 and 

 93,000,000 miles, and no less than 268 minor planets are 

 now on our lists. 



It is to be regretted that books of this kind, written in 

 clear, simple language, are not more appreciated by those 

 responsible for the selection of reading-books for our 

 elementary schools. 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 tcitie to return, or to correspond with the writers of, 

 rejected manuscripts. No notice is taken of anonymous 

 comtnunications. 



[The Editor urgently requests correspondents to keep their 

 letters as short as possible. The pressure on his space 

 is so great that it is impossible otherwise to insure the 

 appearance even of communications containing interesting 

 and novel facts. 1 



On the Constant P in Observations of Terrestrial 

 Magnetism. 



In regard to the quantity P, depending on the distribution 

 of magnetism in a pair of magnets employed for measuring 

 terrestrial horizontal force, for the calculation of which Prof. 

 Harkness, in Nature for August 18, p. 366, gives a simplified 

 expression, may I be allowed to mention that a yet more simple 

 modification of the ordinary formula has been used in the 

 Greenwich observations since the year 1878, in which, the 

 diiference between A and A^ being small, 



P = (logA-logAi)X 



{r^ - r^) modulus 



When the two distances employed are, as is usual, always the 

 same, the factor becomes a constant, being, for r = i "O foot and 

 ;'i = I '3 foot, = 5 '64. The advantage of the formi is that as, in 

 the calculation, the logarithms of A and A^ are first arrived at, 

 their difference multiplied by 5 '64 at once gives P. Mention of 

 this is made in the introduction to the Greenwich Magnetical 

 Observations for 1878, and in those for some following years, 

 although omitted from the more recent volumes. 



William Ellis. 



Royal Observatory, Greenwich, August 24. 



