28 



NATURE 



[November 8, 1S94 



heats of solids, of thermal methods, of those based on 

 :he vapo'jr-pressures of solutions, of the viscosity of 

 liquids, and of methods based on volume-changes. 



The chapter on electrical methods is supplied by Prof. 

 Dr. Ostwald, of the University of Leipzig. The author 

 gives an account of the rise of electro-chemistry and of 

 its development by Berzelius and Hisinger, and of its 

 dominance down to 1S40. It is remarked that, after his 

 first investigations, Berzelius did not undertake any ex- 

 perimental work on the action of electricity upon chemical 

 compounds, .-\fter 1S40 this theory- was found incapable 

 of e.xplaining facts which were being brought to light in 

 the region of organic chemistry, whilst its physical 

 foundations were shaken by the researches of Faraday. 

 More recently, Hittorf, Arrhenius, Helmholtz and others 

 have founded a new electro-chemical theory. Mention 

 is made of the discussion — not yet decided— as to the 

 origin of the current in the pile. The conception of ions 

 as the material conveyance of the current has been gradu- 

 ally introduced since the researches of Clausius, and is 

 taken into account in our views of decomposition. Not less 

 interesting is the account of optical methods. The first 

 part, from the pen of Mr. G. Gladstone, discusses refraction 

 and dispersion ; the second, on spectroscopic methods, 

 is contributed by Prof. W. N. Hartley, F.R.S ; and the 

 third part, on the rotation of the plane of polarisation of 

 light, is by Prof. Pattison Muir. In the part treating of 

 the spectroscopic methods we find studies of the infra-red 

 and ultra-violet absorption spectra, with notices of the 

 researches of V. Schumann, Waterhouse, Crookes and 

 Gladstone. In connection with the absorption spectra 

 — a subject by no me.ins fully explored — we have a 

 notice of Witt's views on the cause of colour in organic 

 compounds. 



.•\mong the elements admitted or supposed, we find in 

 this volume, notices of phosphorus, platinum, potassium 

 rhodium, rubidium, ruthenium, samarium, scandium, 

 selenium, silicon, silver, sodium, strontium, sulphur, | 

 tantalum, tellurium, terbium, thallium, thorium, tin, 

 titanium, tungsten, uranium, vanadium, yttrium, ytter- 

 bium, zinc and zirconium, with compounds or derivatives. 

 The authors and contributors are noticeable for a 

 sobriety of statement ; they do not indulge in premature 

 conclusions and in speculations for which evidence is 

 lacking. 



As regards the elements, the Mendelejeff classifica- 

 tion is adhered to, and in the accounts of their pre- 

 paration the recent results of Moissan have not been 

 overlooked. 



The addenda comprise facts in mineral chemistry 

 which have been observed since the appearance of 

 Vols. 1., II., and III. and the printing off the final proofs 

 of the present volume. The addenda include nothing 

 on organic chemistry ; since to have noticed the recent 

 discoveries in that department would, in the opinion of 

 Mr. Pattison .Muir, have required the addition of many 

 hundred pages. 



On comparing the present work with former diction- 

 aries of chemistry, whether in English or in any other 

 language, its superiority will appear beyond all ([uestion 

 It will be the obvious duty of all universities, colleges 

 &c., at once to add this new edition of " Watts " to their 

 libraries. , 



MO. I 30'3, VOL. 51I 



DISEASES OF TREES. 



Text-Book of the Diseases of Trees. By Prof. R. 

 Hartig, of Munich University. Translated by W. 

 Somerville, Professor of Agriculture and Forestry, 

 Durham College of Science, Newcastle. Revised 

 and edited by Prof. H. Marshall Ward, F.R.S. 

 2 (London and New York: Macmillan and Co., 



1S94.) 

 " T^ER Lehrbuch der Baumkrankheiten von R. 

 J-^ Hartig" has now appeared in English with all 

 the admirable illustrative plates of the second edition, 

 except the coloured plates at the end of the book, which 

 represent spruce and oak wood decomposing under the 

 influence of difi'erent fungi, and are therefore somewhat 

 exterior to the proposed scope of the work, " the diseases 

 of trees." The original, as Marshall Ward states in 

 the preface to the present version, owes its great charm 

 " to the simple method of exposition of the facts and 

 principles conveyed, as well as to the astounding rich- 

 ness of the information it contains. This is unquestion- 

 ably owing to Hartig's prominence as the leading inves- 

 tigator and authority on the fungoid diseases of forest 

 trees." 



The great superiority of Hartig's work in this subject 

 has been acknowledged in France, by the publication 

 there, in 1S91, of a French translation by Profs. Gerschel 

 and Henry, of the Nancy Forest School, which was 

 entirely revised by the author. 



Prof. Somerville, the translator of the jiresent English 

 edition, has followed a complete course of forestry at a 

 German forest school, and has been for some time 

 engaged in forestry instruction at Edinburgh and New- 

 castle. He has already written a valuable little book on 

 the structure of European timbers. The translation of 

 Hartig's book follows the original closely, and is smooth 

 and free from Germanisms. 



The editor. Prof. H. Marshall Ward, whose qualifi- 

 cations for the work need no comment, has written an 

 excellent preface, besides revising the translation and 

 supplying short foot-notes in explanation of all scientific 

 terms, which might puzzle readers who have not studied 

 vegetable physiology very deeply, and in a few cases 

 giving his own opinion where he does not coincide with 

 the authors. 



In the preface, the bold but thoroughly justifiable 

 statement is made that students of agricultural chemistry, 

 or of the physics and chemistry of soils, must thoroughly 

 master the facts of the structure and essential phenomena 

 of life by experimental investigation, and that the 

 chemistry of the soil taken alone is of less practical im- 

 portance. The fact is, that although the want of 

 sufficient suitable chemicals in a soil may render certain 

 tree-growth stunted and unproductive, yet the physical 

 nature of the soil, i.e. its degree of division and hygro- 

 scopicity, and the climate of the locality, are more im- 

 portant than the foiincr to ensure a healthy and vigorous 

 tree-growth ; whilst a good coating of decomposing dead 

 leaves will render a soil, which is chemically and 

 physically poor, capable of producing a fair crop of 

 timber. The influence of earthworms on soils has been 

 dealt with by Darwin, whilst that of bacteria and other 

 low organisms in decomposing organic debris to form 



