558 



NATURE 



[January 21, 19 15 



generation and propagation of electromagnetic 

 waves. There are two chapters which are num- 

 bered ix. and x. in continuation of the chapters 

 of the earlier volumes. The sections are also 

 numbered in continuation of the sections of vols. 

 i. and ii. The fifty-three sections which con- 

 stitute chapter ix. were published originally in 

 the Electrician during 1900 and 1901, and are 

 grouped under the title of "Waves from Moving 

 Sources." Largely by synthetic methods the 

 author constructs the solutions of various cases, 

 discussing in his own way the fundamental ques- 

 tion of the connection between matter and aether. 

 Some interesting remarks are made concerning 

 the investigations of Larmor and Lorentz. The 

 later sections deal with spherical pulses started 

 by a "jerked electron." 



Chapter x. with its forty-one sections occupies 

 about three-quarters of the whole book. It is 

 called "Waves in Ether." The first seven sections, 

 reprinted from the Electrician (1902) form a group 

 of connected discussions in which a deformable 

 aether is assumed along with a constant velocity 

 of radiation through it. The assumptions are 

 found to be compatible if the inductivity and per- 

 mittivity of the aether vary as the density. The 

 remaining sections, some of which appeared 

 originally in Nature, are more of the character of 

 isolated articles, bearing either directly upon 

 electromagnetic theory or upon mathematical 

 and physical problems suggested by its develop- 

 ment. For example, there is a long article on 

 the solution of definite integrals by differential 

 transformation, and one nearly as long on the 

 inversion of operations. Still longer is section 

 534, on the theory of an electric charge in variable 

 motion, probably one of the most important in 

 the whole book. Here, as elsewhere, Dr. Heavi- 

 side strongly affirms the truth of Newton's Third 

 Law of Motion, "an impregnable fundamental 

 principle whose neglect sometimes leads to alarm- 

 ing consequences." Why, he asks at the very 

 end of the volume, is this principle to be taken as 

 fundamental? "Because it is always true when 

 proper examination can be made, and is the guide 

 to fresh knowledge. Besides that, the untruth of 

 the principle in practice would lead to chaos." 



Dr. Heaviside is also a firm believer in the 

 existence of the aether. "Through this ether all 

 known disturbances are conveyed electromag- 

 netically or gravitationally. If the first way, the 

 speed is finite. If the second way, it may also 

 be finite, perhaps with the same velocity. . . . 

 As the universe is boundless one way, towards the 

 great, so it is equally boundless the other way, 

 towards the small ; and important events may 

 arise from what is going on in the inside of 

 NO. 2360, VOL. 94-1 



atoms, and again, in the inside of electrons. 

 There is no energetic difficulty. Large amounts 

 of energy may be very condensed by reason of 

 great forces at small distances. How the elec- 

 trons are made has not yet been discovered. 

 From the atom to the electron is a great step, 

 but is not finality." 



To the elucidation of the deep problems in- 

 volved in this confession of scientific faith. Dr. 

 Heaviside has made great and lasting contribu- 

 tions. The strenuously minded student will find 

 him a stimulating guide through the intricacies 

 of the electromagnetic equations. The book is 

 with great fitness dedicated to the memory of 

 George Francis Fitzgerald. C. G. K. 



THE ASCENT OF SAP IN PLANTS. 

 Transpiration and the Ascent of Sap in Plants. 

 (Macmillan's Science Monographs.) By Dr. 

 Henry H. Dixon. Pp. viii + 216. (London: 

 Macmillan and Co., Ltd., 1914.) Price 55. net. 



PROF. DIXON first became known as an 

 investigator of the problem of the ascent of 

 water in plants by his work in collaboration with 

 Dr. Joly published in the Proceedings of the Royal 

 Society, 1894, and in the Philosophical Transac- 

 tions, 1895, ^"d from that time forward he has 

 with admirable patience and efficiency continued to 

 work at this difficult question. The appreciation of 

 his position as an authority in this department is 

 shown by his having been most appropriately 

 chosen as a contributor to the " Progressus Rei 

 Botanicae," and finally as a writer in the present 

 series of science monographs. 



When a second edition is called for, it is to be 

 hoped that Dr. Dixon will see his way to giving 

 the references to literature as footnotes instead of 

 at the end of the chapters, an arrangement that 

 seems to us to have no practical advantages. The 

 only other criticism of a general kind that we have 

 to offer is on the relative space given to the two 

 main divisions of the subject. There is but one 

 chapter on the "nature of transpiration," while the 

 remainder, consisting of about 200 pages, deals 

 with the ascent of sap. But there is so much to 

 be said on the latter subject that the author may 

 well feel justified in his comparatively brief treat- 

 ment of transpiration. There are many interesting 

 points in chapter i., e.g., the discussion on trans- 

 piration considered as a form of secretion, and the 

 allied question of transpiration in air saturated 

 with moistures. 



Prof. Dixon does not, we think, quite realise 

 the danger of assuming that the stomata are 

 thrown out of action as far as transpiration is 

 concerned by dull light or darkness. But inas- 



