NA TURE 



[May 2, 1907 



It would seem to us, accepting the writer's own 

 account of his intention, that the requirements neither 

 of the student nor of the practical optician have been 

 kept sufficiently clearly in view. It is probably rather 

 to the amateur who wishes to acquire an intelligent 

 appreciation of the main principles of construction of 

 the more important optical instruments that the book 

 will appeal. The practical optician is daily confronted 

 with problems towards the solution of which he will 

 here find little help, while the student who looks for 

 an introduction to the subject will scarcely do well 

 to acquire the elements of optics from a w-ork in 

 which the necessary mathematics are so entirely kept 

 out of sight. For the general reader the volume pre- 

 sents many excellent features, yet even to him we 

 would prefer to recommend Moritz von Rohr's 

 admirable little book, " Die optischen Instrumente," 

 which provides for the non-mathematician a very 

 considerable amount of information in the smallest 

 compass. 



For the rest, the matter is carefully arranged and 

 the explanations of technical points clearly and simply 

 given. The usual portions of the subject are in- 

 cluded — the elementary theory of mirrors, prisms and 

 lenses, the optics of the eye, the microscope, tele- 

 scope, and the photographic lens. There is a chapter 

 also on stereoscopy, in which some of the modern 

 developments are shortly treated. The variable power 

 telescope receives rather more attention than is usual. 

 Tables are given for the calculation of achromatic 

 lenses and of prism combinations, and throughout the 

 book attention has been paid to the furnishing of 

 numerical data. These, however, might easily be 

 rendered more complete — e.g. particulars as to the 

 field of view obtainable at various powers in tele- 

 scopes of different pattern would be of value. Com- 

 plete data are provided for the construction of certain 

 well-known combinations, direct-vision prisms, eye- 

 pieces, microscope objectives, photographic lenses, &e. 

 The provision of numerical information is, indeed, the 

 most characteristic feature of the book, and will 

 render it of value for occasional reference to some 

 who are already familiar with the author's present- 

 ment of the optical theory. 



OVR BOOK SHELF. 

 Die Eisenindustrie. By Oskar Simmersbach. Pp. 



X-H322. (Leipzig and Berlin: B. G. Teubner, 



1906.) Price 7.20 marks. 

 In German technical literature there are excellent 

 exhaustive treatises on the metallurgy of iron, and 

 students' manuals exist in abundance, but Mr. 

 Simmersbach 's work on the economics of the iron 

 trade opens up an entirely new field. The leading 

 principles and practices of the German iron trade are 

 made clear, and a careful study of the information 

 set forth cannot fail to prevent much waste of time 

 and misapplication of energy in the conduct of busi- 

 ness. The various chapters are well worthv of atten- 

 tive study, and the book should find a place in the 

 library of all who have any connection with the iron 

 Industry. 



The first eight chapters give a concise introduction 

 to the technology of iron and steel. Thev deal re- 

 spectively with iron and its alloys, raw materials, 



NO. 1957, VOL. 76] 



blast-furnace practice, steelworks practice, rolling 

 mills, testing of iron and steel, foundry practice, and 

 the testing of cast iron and cast steel. The remain- 

 ing seven chapters, dealing with the economics of 

 iron and steel, are of greater interest. A general 

 sketch of the importance of the world's iron trade is 

 followed by chapters on the world's ore trade, the 

 world's coal and coke trade, the world's pig-iron 

 trade, the world's trade in castings, and the world's 

 trade in malleable iron and steel. The final chapter 

 deals with labour conditions and customs tariffs. 

 The author takes an exceedingly optimistic view of 

 the German coal and iron-ore resources. Germany 

 is, he thinks, richer in iron ores than the rest of the 

 Continental countries put together, and he explains 

 the annual importation of more than six million tons 

 of foreign ores as being the outcome of high rail- 

 way charges, .^t the present rate of coal consump- 

 tion there is, he believes, enough coal in Germany 

 still unworked to last for 3520 years. These figures 

 contrast strongly with his pessimistic views of the 

 available resources of other countries. Prophecies as 

 to the future of the world's iron trade are, however, 

 of little moment. 



The chief value of the author's work is in the 

 abundance of admirably arranged statistical material 

 regarding the present condition of the iron and steel 

 industries, and in the evidence amply afforded of the 

 manner in which science has superseded the old rule- 

 of-thumb methods of carrj'ing on operations at iron 

 and steel works. .A. chapter on trusts, cartels, and 

 syndicates would have been a useful addition to the 

 work, and the absence of an index is to be deplored. 



,4 Text-book of Fungi. By G. Massee. Pp. xi + 427. 

 (London : Duckworth and Co., 1906.) Price 6s. 



net. 

 The fungi constitute numerically the most extensive 

 group of plants, and at the same time they present 

 the largest number of unsolved problems ; this, too, 

 despite the fact that, as the author says, our know- 

 ledge has increased by leaps and bounds. 



Mr. Massee plunges at once in medias res, and 

 proceeds to describe modern cytological developments, 

 their legitimate and strained applications, and certain 

 lines of inquiry pursued by Marshall Ward. Recent 

 work has widened our knowledge of conidia, spores 

 of various kinds, and other methods of reproduction. 

 The author has introduced the salient facts both of 

 sexual and asexual reproduction, but fails to offer a 

 logical definition or a practical limitation of the terms 

 spore, sporophore, &c. The chapter on sexual re- 

 production contains useful summaries of Blakeslee's 

 account of the Mucorinese, Thaxter's investigations of 

 the Laboulbeniaceae, as well as Dangeard's and 

 Blackman's researches. The author's views on 

 parasitism in fungi are set forth, and reference is 

 made to experiments on similar lines by Miss Gibson 

 and Mr. E. S. Salmon, the latter of whom has con- 

 tributed the chapter on "biologic forms." Closely 

 allied with the spread of disease, which provides the 

 opportunity for noting the insidious danger of 

 hibernating mycelium, is the subject of legislation. 

 Mr. Massee enunciates his arguments, which are 

 mainly to show that, unless it is exceedingly drastic, 

 legislation to prevent the introduction of plant 

 diseases through imported plants and seeds would be 

 useless. 



On the subject of classification, the opinion of the 

 author as an acknowledged exponent is especially 

 valuable, and the reader will find clear, and we think 

 convincing, reasoning in favour of the acceptation 

 of Brefeld's main groupings. The persona! views on 

 phylogeny appearing earlier in the book should be 



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