July 6, 1905] 



NA TURE 



219 



two great monographs of the Rhizopods and Heliozoa, 

 are here presented in a form more accessible to the 

 student. About fifty species and varieties are de- 

 scribed and figured, the majority being peculiar to 

 deep lakes, the others characteristic of, though not 

 confined to, deep lakes. 



On looking over the diagnoses of the species, it 

 cannot fail to be remarked that many of them are 

 distinguished by very trivial differences from other 

 known species. Considering the intolerable burden of 

 synonymy in zoological nomenclature which results 

 from the practice of describing species on insufficient 

 grounds, it is a pity that Dr. Penard should have 

 conferred a specific name upon a form (Difflugia 

 curvicaulis, Penard) which he naively admits he re- 

 gards as scarcely even a fixed variety. Other in- 

 stances are not wanting in the volume of species 

 which seem to be of very little value. It is obvious 

 that he makes insufficient allowance for the recognised 

 variability of the species of the group. He puts too 

 much reliance on size as a specific character, and gives 

 an exaggerated value to minute differences in the size 

 and form of the scales which encrust many species. 



Making all allowance for the slight differences on 

 which he separates the abyssal species from the re- 

 lated species of shallower waters, it appears that there 

 is really some considerable amount of peculiarity 

 among the abyssal Sarcodina. Species tend to appear \ 

 in the abyssal region under different forms or varieties 

 from those found elsewhere. We would ask, how- 

 ever, whether this peculiarity is any greater than one 

 would expect from the influence which must be 

 exerted by the very different environment upon the 

 individuals produced in this region ? 



Of interest in this country is Dr. Penard's assertion 

 that some representatives of the abyssal fauna of the 

 Swiss lakes have been found by him in Loch Ness. 

 The difficulty of accounting for the passage of abyssal 

 forms from one lake to another is just touched upon, 

 and dismissed with the short statement that several 

 of the species have also been found at the margins of 

 the lakes, as well as in the depths. One is tempted 

 to make another explanation of this fact, and say 

 that it proves that they are not peculiarly abyssal. 

 Dr. Penard does not say whether he regards this 

 coming to the shore as a normal mode of migration 

 of abyssal species. 



In the special case of Loch Ness, there are facts 

 which make it difficult to believe that the abyssal 

 Rhizopods are peculiar species. No abyssal species 

 of any other class has yet been found in Loch Ness. 

 Some of the forms which are regarded as purely 

 abyssal in the Swiss lakes are found in the shallow 

 bays of many Scottish lochs, and even in peat bogs. 

 This may prove an interesting fact in distribution if 

 it can be shown that species which are superficial in 

 Scotland have to descend to some depth in Switzer- 

 land in order to find congenial conditions of tempera- 

 ture. Among Dr. Penard's abyssal forms which have 

 been found in Scottish moss may be mentioned Helio- 

 pera petricola, var. amethystea, Penard, and Cypho- 

 deria ampulla, var major, Penard. 



Making due discount for his too high appreciation 

 of minute differences, and appraising his species at 

 NO. 1862, VOX. 72] 



our own value, this volume is valuable to students of 

 the Sarcodina, as there is no question of Dr. Penard's 

 painstaking accuracy of observation. His descrip- 

 tions are clear and concise, while the illustrations in 

 the text are excellent. 



STEAM TURBINES. 

 (i) Steam Turbines, with an Appendix on Gas Tur- 

 bines. By Dr. A. Stodola, of Zurich. Translated 

 from the second revised and enlarged German 

 edition by Dr. L. C. Loewenstein. Pp. xvi + 434; 

 illustrated. (New York : D. Van Nostrand Com- 

 pany ; London: .Archibald Constable and Co., Ltd., 

 1905.) Price 21s. net. 

 (2) Bail der Dampfturbinen. By Prof. A. Musil. 

 Pp. 6 + 233. (Leipzig: B. G. Teubner, 1904.) 

 Price S marks. 

 (O'T^'HE steam turbine has for some years now, 

 J- thanks to the inventive genius of Mr. Parsons, 

 become a formidable rival of the reciprocating steam- 

 engine on land, and the past three years have seen a 

 rapid increase in its use for marine purposes. On 

 cross-channel steamers there is no doubt that in a few 

 vears it will completely oust its rival, while the adop- 

 tion of this type of engine for two of the Allan line 

 steamers, and the decision to use steam turbines for 

 propelling the great Cunarders now being built, prob- 

 ably herald the approach of the day when on these 

 big liners also the reciprocating marine engine will be 

 entirely displaced. 



It is not surprising, therefore, that there has grown 

 up a rapid demand for good text-books on the steam 

 turbine in which both the theory and the constructive 

 details of the numerous types now on the market are 

 fully dealt with. In addition to numerous papers and 

 articles which have been printed in the Transactions 

 of our leading engineering societies and in the 

 technical journals, we have had two editions of Mr. 

 Neilson's book, and now, by this English translation, 

 the latest edition of Dr. Stodola 's classic work is made 

 available to British engineers. 



In his preface to the second edition. Dr. Stodola 

 points out that he has been able in the period which 

 elapsed since the issue of the first edition to investi- 

 gate experimentally several important problems un- 

 touched in the first edition, as, for example, the fric- 

 tional resistance of turbine wheels in^, air. In the 

 first section, after dealing with the elementary theory 

 of the steam turbine, a concise and clear classification 

 is given of the various types which have so far been 

 practically successful. The more advanced thermo- 

 dynamic problems which are met with in the theory 

 of the steam turbine form the subject of the second 

 section, and details are given of a series of valuable 

 experiments on the flow of steam from orifices ; these 

 experiments are of great importance, and the results 

 are very striking, and will undoubtedly prove of great 

 value to those engaged in the design of diverging 

 nozzles for turbines. In connection with this chapter, 

 MoUier's diagrams for the properties of saturated 

 steam are explained ; these diagrams have been re- 

 produced, and, for the English edition, similar 



