lOO 



NA TURE 



[November 30, 1899 



here no living organisms have been found. It is purely 

 azoic ; the reason for the want of life is, according to the 

 author, the want of oxygen and the abundance of carbonic 

 acid. 



There is, in fact, no special deep-sea fauna found in this 

 large tract of water. 



Turning to the terrestrial mammalia, the author comes 

 to the conclusion (elaborated in a special and highly 

 interesting chapter) that their range to-day is in thorough 

 agreement with the distribution of land and water. The 

 Mediterranean southwards and the Bosphorus westwards 

 form barriers which divide faunas. This is illustrative of 

 what is apt to be a common error in text-books of 

 zoology. When Mr. Sclater originally divided up the 

 earth into zoological regions, he did not profess to do so 

 for more than the Passerine birds, though his conclusions 

 were shown later by himself and by others to apply to 

 other groups also. They do not, however, in the least 

 apply to various invertebrate groups; and in dogmatically 

 dividing the world into the Sclaterian regions, the writers 

 of some text-books have entirely lost the prime object of 

 such a regional division. The more modern Eutherian 

 mammals are controlled in their range by what are 

 largely existing barriers ; the more ancient molluscs show 

 in their distribution the non-existence of such barriers in 

 ancient times. Dr. Kobelt dwells upon the distinctness 

 of northern Africa from Europe so far as concerns its 

 mammalian inhabitants. He is disposed to dismiss the 

 Gibraltar monkey as truly indigenous to that peninsula, 

 though admitting the occurrence of fossil allies in 

 European strata of Pleistocene and Pliocene age. 



On the whole, however, we are not certain that Dr. 

 Kobelt has taken so fortunate an instance as he might 

 have done to illustrate the effects of modern barriers in 

 the dispersal of mammals. It is perhaps a little too 

 strong, in the face of the lists which he gives, to state of 

 the Straits of Gibraltar and the narrow passage opposite 

 to Carthage that they are "faunistic boundaries of the 

 first rank." The division between the arctic and the non- 

 arctic parts of the pala^arctic region are more easily 

 defined from their mammalian indigenes. 



Dr. Kobelt's'j book is closely packed with solid fact, 

 and there is no more speculation than is necessary to 

 give prominence to such generalisations as appear to him 

 to be the legitimate outcome of his laboriously collected 

 material. This has been amassed from the most diverse 

 sources ; and the author by no means disdains the older 

 writers, even the ancients being laid under contribution. 

 We commend the book to the serious student of zoo- 

 geography only, for it is emphatically not to be trifled 

 with in an arm-chair. jr £ g 



Perry, D.Sc, F.R.S. 

 Macmillan and Co., Ltd.. 



A TEXT-BOOK OF HEAT MOTORS. 

 The Steatn Engine and Gas' and Oil Engines. By John 

 Pp. viii + 646. (London : 

 1899.) 



T^HIS is one of the jbest books which has been pub- 

 *- lished in this country on the steam engine and 

 other heat motors. The method and style is thoroughly 

 characteristic of Prof Perry. Many will no doubt object 

 to the order of arrangement of the various chapters, and 

 NO. 1570, VOL. 61] 



will be inclined to think the author has put the carl 

 before the horse ; the author will probably reply that the 

 book was not written for the beginner, but for advanced 

 students. 



There is something to be said for the plan adopted ; if 

 a text-book for students, engaged during the day in 

 practical engine work, is given up in its early chapters 

 almost entirely to the properties of steam and thermo- 

 dynamic problems, there is great risk that the student 

 will be discouraged and eventually give up the attempt 

 to improve his knowledge of the principles underlying 

 the working of heat motors. 



The author's plan is to deal first with the more practical 

 details, in the hope probably that in mastering these the 

 student will find out what he lacks and what he needs of 

 thermodynamics and kindred subjects. Granted this, 

 it is still a little difficult to see that an improvement 

 would not be effected by putting Chapters xv., xviii. and, 

 xix. on methods of calculation, on temperature and 

 heat, and on the properties of steam, earlier in the book. 

 This is shown by the necessity of a footnote on p. 99 to 

 explain the way in which the total heat required in 

 evaporating a pound of steam is determmed. 



Chapter ii. is devoted to description of cylinders, 

 pistons, valves, frames, &c., of what the author calls the 

 commonest form of steam engine, but as the details ex- 

 plained include parts of steam turbines, the title is hardly 

 happy. The illustrations in this chapter are extremely 

 good and complete. 



Chapter iii. deals with the value of expansion, and the 

 author points out, as. a result of his calculations, that 

 there are limits of economic expansion, and how easily 

 the Willan's law can be deduced from such calculations. 

 Chapter iv. describes thejndicator, its construction and 

 the proper way to use it, and the errors it is liable to. 

 Then, in the following chapter, come a most valuable 

 series of exercises on calculations from indicator cards. 



One of the chief merits of the book, apart from the fact ' 

 that it is so thoroughly up to date in all its information 

 and methods, is the way in which almost every chapter 

 is filled with numerical exercises ; any student genuinely 

 working these out for himself cannot fail to become 

 thoroughly master of the main problems confronting the 

 student of heat motors. 



In this chapter again (v.) we have a little awkwardness 

 introduced from the particular arrangement adopted by 

 the author. One of the exercises is the drawing of a 

 ^0 diagram, and no explanation of this has been 

 given, the reader is referred for explanations to a much 

 later chapter of the book. We fear the student is not 

 likely to start with much knowledge of entropy, and 

 will therefore probably skip these sections. 



The next eight chapters are devoted to the mechanical 

 details of valves, governors, air pumps, boilers and their , 

 fittings and accessories. 



The first fourteen chapters may be said to mainly deal 

 with the mechanical details of engines and boilers ; while 

 the rest of the book is devoted to what may be called 

 theory and principle. 



In Chapter xvi. the author deals with the cost of pro- 

 duction of energy and the efficiency of various types of 

 motors, a most complete and valuable chapter full of 

 good examples. Then come some chapters on tem- 



