NA TURE 



[January 9, igo8 



character. The author must not think, therefore, that 

 we speak unfavourably of his \vorl< because of its 

 novelty. The true e.xplanation of physical phenomena 

 will sound exceedingly novel, we have no doubt, when 

 it is first put forward. It may be that in the author's 

 mind there is a germ of an idea which deserves 

 developing. But if he wishes this to be recognised it 

 would be well if he were to get some friend to assist 

 him in the process. 



The main aim of the book is to reduce all " forces " 

 to one origin ; and the secret by which it is done is 

 the recognition of the "polarity of matter." Con- 

 sidering the thoroughgoing attempts of Sutherland 

 and others to explain gravitation by means of polar 

 svstems of electrons, he would be a rash man who 

 should say that the author's idea is absolutely chim- 

 erical. Whether or not he is qualified to develop it 

 may perhaps be learned from the following extracts : — 



" When the magnet is a straight bar . . . the dis- 

 tance between its pole being 2a . . . the magnetic 

 force is 3'I4 times the gravitational force. If the mag- 

 net be bent into the form of a horse-shoe so that the 

 distance between its poles is a, the magnetic force is 

 12-5 times the gravitational force. . . VVhen the poles 

 of the magnet come together the force is unity. . . .'" 



" The position of a fragment of iron in a magnetic 

 field mav therefore be defined as tangential to an 

 ellipse of which the magnetic poles are the foci." 



" The force of attractive interest in each of two 

 bodies forming the poles of an electric force is a 

 constant quantity, and when the force radiates equally 

 in all directions its magnitude is gravity." 



" In all cases of magnetisation by means of an 

 electric current, certain waves proceed from the cur- 

 rent by w-hich the effect is produced. These waves are 

 commonly called Hertzian waves." 



If the seeker after novelty finds in the above ex- 

 tracts the particular kind of novelty for which he 

 seeks, we cordially commend the book to him ; and 

 we wish him greater success in unravelling its mean- 

 ing than we have attained. 



WM Bees, Wasps and Ants, and other Stinning 

 Insects. Bv Edward Saunders, F.R.S. With 

 numerous illustrations in the text and four coloured 

 plates by Constance A. .Saunders. Pp. xiii+144. 

 (London : Routledge and Sons, Ltd., n.d.) Price 

 2S. 6d. 



Since the death of Frederick .Smith, probably no man 

 has given more attention to the study of our British 

 Hymenoptera Aculeata (the section of the order which 

 contains stinging insects, such as bees, wasps, and 

 ants, &c.) than Mr. E. Saunders. This order of in- 

 sects is much less hackneyed than the Lepidoptera or 

 Coleoptera, and Mr. Saunders's work will be very 

 useful to beginners commencing the study of perhaps 

 the largest order of insects of all, and also of the most 

 interesting section, for there are only four groups of 

 insects known which include species living in organised 

 communities, three in Hymenoptera — bees, wasps, and 

 ants — and only one in Neuroptera — the termites, impro- 

 perly called white ants. The non-aculeate Hymenop- 

 tera, not here dealt with, are far more numerous, and 

 are very imperfectly known or studied at present ; they 

 comprise the sawflies and gall flies, and also the 

 ichneumons, and other parasitic insects, hundreds of 

 which are of very small size, including among them 

 the smallest known insects. 



But it will be sufficient for most entomologists who 

 are inclined to studv Hvmenoptera to follow the lines 

 laid down by Mr. Saunders for the examination of 

 the structure and habits of the more familiar and less 

 difficult group of Hymenoptera .Aculeata. The infor- 

 mation given, though, of course, much condensed, is 



NO. 1993, 'VOL. 721 



well arranged and thoroughly trustworthy, besides 

 being expressed in an attractive manner. The last 

 chapter, " On Structure," with a good diagram and 

 clear descriptions, will be particularly useful, for 

 nothing is more troublesome to an entomologist taking 

 up the study of an order or group of insects unfamiliar 

 to him than the absence of a clear explanation of 

 the terms applied to the various details of insect 

 structure. 



Das Problem der Scliiuingungserzeuguiig. By Dr. H. 



Barkhausen. Pp. iv + 113. (Leipzig; S. Hirzel, 



1907.) Price 4 marks. 

 The author of this book discusses the conditions under 

 which an instrument or piece of apparatus can produce 

 undamped vibrations when the source of energy does 

 not vary periodically. 



The organ pipe and violin string illustrate the 

 phenomenon in the case of vibrations produced by 

 mechanical means. For the mathematical theory, 

 however, electrical vibrations are the most convenient, 

 and as the problem of creating undamped electrical 

 vibrations is of present-day importance in wireless 

 telegraphy, the greater part of the book is devoted to 

 its consideration. 



The first result obtained is that a necessary con- 

 dition for the production of permanent vibrations 

 is the presence of a variable alternating resistance, 

 self-induction or capacity in the current system. The 

 variation of the resistance may be due to external 

 action, as in the microphone and in a new arrange- 

 ment called the resonance interruptor, which is 

 capable of giving high frequencies, or it may arise 

 from the current flowing through the apparatus as 

 in the electric arc. 



The author makes frequent use of graphical 

 methods, especially in the discussion of three different 

 types of vibration which can be produced with the 

 arc. These are investigated separately, and compared 

 with regard to their capacities for resonance, high 

 frequency, and performance of work. The questions 

 of stability show that permanent vibrations can be 

 obtained only when the interval for re-kindling after 

 extinction increases more rapidly at first than it does 

 afterwards. Various methods are given by which 

 this can be ensured. 



The book concludes with a chapter on mechanical 

 vibrations, particular attention being paid to those 

 produced bv friction. On the whole, the exposition 

 is good, and we can confidently recommend the book 

 to those who wish to obtain a grasp of the principles 

 of the subject. H. B. 



Album de Aves Aniaconicas. By Dr. E. A. Goeldi. 



(Para : Museu Goeldi, 1907.) 

 We have been favoured with a copy of the third and 

 final fasciculus of this superbly illustrated work, of 

 which the first part was noticed in our issue of 

 .August 22, 1901. The present fasciculus includes 

 plates 25-48, which are executed in the same first- 

 class style as their predecessors, and a re-issue of the 

 descriptions of the entire series, together with several 

 well-arranged indices. We can add little in the way 

 of commendation to what has been already written in 

 our notices of the two earlier issues. Throughout the 

 work the figures are for the most part w^ell drawn, 

 and coloured with such a near approximation to 

 nature as to render the various species easily recog- 

 nisable. That the work will tend to promote the 

 study of Brazilian ornithology cannot be doubted, 

 and the author is to be heartily congratulated on 

 having given to the world such a splendid series of 

 portraits of the most striking representatives of a 

 tropical bird-fauna. 



