February 21, 1901] 



NA TURE 



393 



OUR BOOK SHELF. 

 Die moderne Entwicklung der elektrischen Principien. 



Fiinf Vortriige von Prof. Dr. Ferd. Rosenberger. Pp. 



lii + 170. (Leipzig : Johann Ambrosius Barth, 



1898.) 

 These lectures formed a course given to school teachers 

 at Frankfort during the Easter vacation, 1897. Published 

 in book form, they furnish an excellent, though brief, 

 historical survey of the development of electrical theory 

 during the past three centuries. Of all those who have 

 aided in this development, probably none played a more 

 important part than Faraday, for it was he who really 

 laid the foundation of the immense structure of modern 

 theory. This is fully recognised by the author of the 

 present volume, who gives due prominence to the work 

 of Faraday and its influence in the development of 

 electrical principles. 



The first two lectures are occupied with the variolas 

 forms of fluid theory of electric action in vogue down to 

 the early part of the nineteenth century. Beginning at 

 the time of William Gilbert, who may be said to be the 

 first to make any attempt at a physical explanation of 

 electric attractions, we are led through a long series of 

 writings extending to the time when Ampere stated the 

 laws of the magnetic action of electric currents, and 

 brought the subject into the state in which it was found 

 by Faraday. The whole of the third lecture is devotfed 

 to the life and experimental work of Faraday, and the 

 great change which he brought about in electrical theory 

 by his introduction of the notion of lines of force. How 

 Faraday's method was so successfully followed by Max- 

 well, Hertz and others is ably described in the fourth 

 lecture. In an amusing section which here follows, and 

 the significance of which is obvious, the author describes 

 the astonishment of the inhabitants of Mars at the 

 wonders of a railway system established there by an en- 

 terprising company of earth-folk, and the elaborate dyna- 

 mical theories with which the wise men of that planet 

 sought to explain the phenomenon. The fifth lecture 

 contains some exposition of the fundamental principles 

 of mechanics and their relations to electricity. The book 

 is throughout written in very readable style, and its value 

 is much enhanced by numerous extracts from original 

 papers. With the exception of certain instances of mis- 

 spelling, notably in extracts from English writings, it is 

 free from inaccuracies. 



The Birds of Africa. By G. E. Shelley. Vol. ii. Part 2. 

 (London : R. H. Porter, 1900.) 



In this portion of his great undertaking. Captain Shelley 

 commences with the genus Promerops and concludes 

 with the pipits, so that he is still far from coming to the 

 end of the Passerines. In the seven exquisite coloured 

 plates with which it is illustrated, Mr. H. Gronvold fully 

 maintains the high standard of their predecessors, and 

 the text is as full and complete as in the earlier parts. 



In his preface the author takes occasion to explain 

 the somewhat unusual arrangement of the Passerines he 

 has seen fit to adopt. "I begin," he writes, "with the 

 Passeriformes and follow on with the Piciformes. The 

 two families of these separate orders which appear to me 

 most nearly allied are the swallows and the swifts, so as 

 I end the Passeriformes with the Hirundinidas it entails 

 beginning the classification with the Oligomyodae." This, 

 of course, renders matters perfectly clear. But, we ven- 

 ture to think this half-hearted approximation of the 

 swifts to the swallows is begging the question. Either 

 they are nearly allied or they are not. If the former be 

 the case, they should be placed in the same order. If 

 the latter, the superficial resemblance between the two 

 groups is entirely due to adaptation, and they should be 

 kept as far apart as possible. 



On this point we may quote from Prof. Newton 



NO. 1634. VOL. 63] 



(" Dictionary of Birds") that "it should be always and 

 most clearly borne in mind that, though so like swallows 

 in many respects, the swifts have scarcely any part of 

 their structure which is not formed on a different plan ; 

 and, instead of any near affinity existing between the two 

 groups, it can scarcely be doubled by any unprejudiced 

 investigator that the Cypselidie not only differ far more 

 from the Hirundinidse than the latter do from any other 

 family of Passeres, but that they belong to what in the 

 present state of ornithology must be deemed a distinct 

 order." 



While, therefore, we maintain that the author has been 

 ill advised in his departure from the ordinary classifica- 

 tion of the Passerines, this in no wise detracts from the 

 value of his work in other respects. R. L. 



One Thousand Problems in Physics. By William H. 



Snyder, A.M., and Irving O. Palmer, A.M. Pp. 142. 



(Boston : Ginn and Co., 1900.) 

 These problems are simple numerical exercises, mostly 

 of an elementary character, on hydrostatics, "tenacity 

 and elasticity," statics and dynamics (including gravita- 

 tion and pendulums), light, sound, heat, expansion of 

 gases, magnetism and electricity. Such a collection of 

 questions should be of much use for class-room exercises. 

 The best way of learning the fundamental principles of 

 elementary physics is undoubtedly to practise making 

 numerical calculations with them, and the large number 

 of questions will enable the book to be used with different 

 classes. Many of the questions could almost be used as 

 oral exercises. 



A few questions strike us as being somewhat am- 

 biguously stated. Thus : " A boat weighing 2 tons is 

 moving at the rate of 10 miles per hour when the engine 

 breaks. If the coefficient of resistance of the water is 

 ?, how far will the boat go before it stops?" Even if it 

 is not considered necessary to specify the law of variation 

 of the resistance with tlie velocity, the units in terms of 

 which the coefficient of resistance expressed should be 

 given, for the result will depend on whether this coeffi- 

 cient represents •= of a ton at a velocity of i mile per hour 

 or 5 of a pound at a velocity of i foot per second. 

 Again : " Two strings 6 and 10 feet long, meeting at a 

 point and making an angle of 60^, support a 50 lb. weight. 

 What is the tension on each string?" Here the result 

 depends, not on the lengths of the strings which are 

 given, but on their separate inclinations to the vertical 

 which are not given and cannot be found without further 

 data. The teacher will have little trouble in avoiding; 

 these questions. 

 Peach-leaf Curl : its Nature and Treatment. By Newton 



B. Pierce. {Bulletin No. 20, U.S. Department of 



Agriculture ; Division of Vegetable Physiology and 



Pathology.) Pp. 204 ; plates 30. (Washington, 1900.) 

 The disease known as peach-leaf curl is due to a fungus 

 C'aS^&di E.voascus deformans {B&r\i.), and seems to be more 

 or less common and destructive wherever peach-trees 

 are grown. It is almost confined to the peach and 

 nectarine and their derivatives ; and although its country 

 of origin is uncertain, it has long been known in Europe, 

 and latterly elsewhere. In some countries, as in New 

 Zealand, it has almost extirpated the peach-tree of late 

 years, while the losses from the disease in the United 

 States are said frequently to amount to several thousand 

 dollars annually. The volume before us deals with the 

 subject with the usual American thoroughness. The 

 fungus itself, and the diseased condition of peach-leaves 

 induced by it, are fully described and illustrated, as well 

 as the best means of counteracting its ravages, chiefly 

 by spraying the trees. Although the book is written 

 primarily for the benefit of peach-growers in the United 

 States, it is well worthy of the attention of fruit-growers 

 in other countries where peach-trees are infested by the 

 disease. 



