January 30, 1902J 



NA TURE 



295 



cess has not yet been reached. While the application of 

 the theory to the solar system is kept mainly in view, the 

 evidence of its truth afforded by observations further 

 afield is by no means neglected ; but no attempt is made 

 to trace the story of celestial evolution generally, or to 

 state the various stellar stages through which the sun 

 itself must have passed. Thus, for the most part, only 

 familiar ground is traversed, and the chief value of the 

 book as a contribution to the literature of the subject lies 

 in the clearness of e.xposition and wealth of illustration. 



The maintenance of the sun's heat and the principle of 

 the conservation of moment of momentum are treated in 

 a specially lucid manner, and the appendices dealing 

 more fully with these questions greatly enhance the value 

 of the book to students. 



Objection might be made to the use of the term " fire 

 mist " as applied to the original nebula, since it was not 

 necessarily an incandescent mass, and consequently also 

 to the extension of the theory which attributes this nebula 

 to the collision of two dark bodies. As a minor objection, 

 the view that the sun's photosphere is composed of par- 

 ticles of carbon cannot yet be regarded as the demon- 

 strated fact which the author seems to suppose. A curious 

 error, occurring on p. 377, may also be mentioned ; it is 

 stated that the discovery of helium in the sun in 1S68 was 

 made during an eclipse, whereas the main point of the 

 observation to which reference is made was that it was 

 made without an eclipse. 



There are numerous excellent illustrations, many of 

 them from photographs ; but the descriptions are in some 

 cases quite inadequate. Thus, Figs. 43, 44 and 54 will 

 only be intelligible to those who have a fair acquaintance 

 with astronomical spectroscopy, and the numerous photo- 

 " graphs of nebula? appear to have been distributed almost 

 at random. 



Monograph of the Cociidac of the British Isles. By 

 Robert Nevvstead. \"ol. i. Pp. .\ii -I- 220. Plates 

 A-E, 1-34. (London : Ray Society.) 

 Thk Coccidfe, or scale-insects, are of great importance 

 horticulturaliy and economically, for although some 

 species yield important products, such as lac and cochi- 

 neal, others are among tlie most destructive pests of our 

 orchards and gardens, being peculiarly injurious to plants 

 grown Under glass. Mr. Newstead, himself a practical 

 gardener, has devoted many years to their study, and 

 has given us the results of his painstaking investigations 

 in the present work. He admits about ninety species and 

 varieties of Coccidie as occurring in the British Islands, 

 belonging to eight of the twelve subfamilies at present 

 recognised, the other four being at present unrepresented 

 in Britain. The systematic part of the first volume deals 

 only with the first subfamily, the Diaspin;e, to which Mr. 

 Nevvstead refers eleven genera and thirty-seven species. 

 A very full introduction is prefixed to the volume, dealing 

 with the structure and habits, parasites, enemies, &c., of 

 the Coccid;e, and practical observations on the best means 

 of coping with their ravages, and full directions for col- 

 lecting and preserving. Among the most original of the 

 author's observations are those relating to birds as 

 •destroyers of Coccida:. 



Till recently the Coccidx' have been one of the families 

 of insects most neglected by British entomologists, and 

 Mr. Newstead's admirabk- monograph adds another to 

 the important series of works on neglected groups of 

 insects for which we are indebted to the Kay Society. 

 There is still, however, much work to be done before our 

 knowledge of the insects of the British Islands can be 

 considered to be anything like complete, especially, per- 

 haps, among the parasitic Hymenoptcra, which have been 

 strangely neglected by most entomologists, notwith- 

 standing their vast number and variety, their beauty, and 

 their economic importance in keeping down the numbers 

 of all kinds of insect pests. This neglect may perhaps 



NO. 1683, VOL. 65] 



be accounted for, however, by the small size of the great 

 majority of the species, many of which, including some of 

 the most curious and beautiful, are among the smallest 

 insects known. But we hope to see these and other 

 neglected groups of insects gradually worked out, on 

 similar lines to those followed by Mr. Newstead in the 

 present work. 



Le Sel, les Salines ct les Marais Sijlants. Par A. 



Larbaletrier, Professeur a I'Ecole d'Agriculture de 



Grand- Jouan. Pp. 166. (Paris : Masson et Cie ; 



Gauthier Villars. No date.) 

 This volume is one of the " Encyclop^die Scientifique 

 des Aide-Memoire," a title which sufficiently expresses its 

 scope. .'Vfter a brief description of chlorine, sodium 

 and the properties of sodium chloride, the methods of 

 production of salt from sea-water on the coast of France 

 are described, followed by short accounts of the treat- 

 ment of the mother liquors of crystallisation for bromine, 

 of the principal European salt mines, of the production 

 of salt from saline springs, and of the Stassfurt deposits. 

 The book concludes with a description of the impurities 

 and analysis of salt, statistics of production in various 

 countries, and of the use of salt in food, agriculture and 

 medicine, and, lastly, a bibliography — perhaps the most 

 important part in a work which is chiefly a compilation 

 of facts obtained from other sources. 



An encyclopedic article of this description, published 

 in a handy form, will be useful provided the data given 

 can be relied upon. Unfortunately, in this instance this 

 is not always the case ; a number of misprints occur in 

 the figures in the tables, misstatements are made in the 

 chemical details, and names of places are misspelt. On 

 the other hand, the methods of mining salt in the 

 principal European mines and the production of salt 

 from sea-water and saline springs in France are ade- 

 quately described, and the book is written in a readable 

 form, sufficiently illustrated and well printed. 



T. S. D. 



Elementary Ophthalmic Optics, including Ophthalmo- 

 scopy and Retinoscopy. By J. H. Parsons. Pp. 162. 

 (London : J. and A. Churchill, 1901.) Price bs. 6d. 

 A SOUND statement of the optical principles involved in 

 ophthalmology, which nevertheless does not require a 

 knowledge of higher mathematics, and which is confined 

 within reasonable limits, has no doubt been long sought 

 by students of this special branch of surgery, and in 

 " Elementary Ophthalmic Optics," now under notice, 

 they will find a trustworthy exposition of the laws affecting 

 the refraction of the eye. The book is well printed and 

 the diagrams are large and clear ; it seems a pity, perhaps, 

 that the author was not bold enough to depart from the 

 conventional letters used in optical formuUe, which, such 

 as /,/i, /,',//, become liable to confusion, though it is 

 difficult to suggest better symbols offhand. 



The student should have been warned that the equation 

 //.,= F-' (p 14), if applied in the case of parallel rays 

 proceeding from infinity, becomes indeterminate. The 

 equations proved in chapters iv. and v. become exceed- 

 ingly wearisome, important though they are, but a few 

 illustrations of their application at the time would relieve 

 the monotony, which might frighten the more practical 

 man from continuing his reading to the later portions of 

 the book, where their results are made use of and where 

 stress is laid on several most important points not usually 

 explained or mentioned in works on ophthalmology. It 

 is not altogether clear where all the distances given for 

 Listing's schematic eye are measured from ; also in an 

 earlier and a later page the foci of the aphakic eye are 

 given differently, leading to confusion in the mind of a 

 careful reader. Chapter vii. brings into prominence some 

 very essential facts in relation to the size of the image 

 formed in the ametropic eye and the effect of spectacles 



