April 12, 1900] 



NA TURE 



56: 



with motion, gravitation, inertia and energy, all units 

 measurements and numerical examples being expressed 

 in the metric system. Following these are sections 

 treating of the elementary phenomena of heat, light and 

 electricity. Magnetism, however, strangely enough, 

 appears to have been entirely neglected, but no state- 

 ment is made in explanation of this somewhat unusual 

 omission. The arrangement and style of both text and 

 illustrations are very good, the only objectionable feature 

 being the ambiguity of a few of the mathematical signs, 

 this being probably explained by the statement of the 

 author that French types were used in this book. Some 

 240 illustrations add considerably to the utility of the 

 volume. 



Part iii., " Practical Chemistry," presents, in the form 

 of a number of described experiments, the mode of 

 preparation and properties of the more common elements 

 and simple compounds. In addition to the actual de- 

 scriptions of these bodies, much correlative matter is also 

 included as to their distribution and economic use. A 

 noticeable omission, from the reader's point of view, is 

 the fact that no equations representing the preparations 

 and reactions of the various substances are given in the 

 text. A collection of equations is, however, given in an 

 appendix at the end of the volume, but it is specially 

 mentioned that the matter contained in this appendix is 

 beyond the scope of the examination. Seeing that this is 

 the third year of the pupil's training, and considering the 

 important manner in which chemical equations enable a 

 student to more easily understand the nature of a re- 

 action by showing at a glance how the several constituents 

 of a mixture arrange themselves, it is difficult to agree 

 with such an omission. The experiments themselves are 

 well chosen, and are usefully illustrated by numerous 

 cuts of the apparatus in position. Each substance is 

 discussed under the headings : — (i) Preparation ; (2) 

 Physical properties ; (3) Chemical properties ; (4) Oc- 

 currence and Uses. 



By G. 



Masson 



By Dr. 



L Echappement dans les Machines a vapeur. 



Leloutre. Pp.156. (Paris : Gauthier-Villars. 



and Co., 1900 ) 

 Produits aromatiques ; artificiels et nattirels. 



G. F. Jaubert. Pp. 169. (Same publishers.) 



These two volumes are the latest additions to the com- 

 prehensive series published as the Encyclopedie scien- 

 tifique des Aide-Memoire. M. Leloutre has for many 

 years carried on experimental and analytical researches 

 upon steam engines, with particular reference to the con- 

 dition of the steam in a cylinder during compression and 

 exhaustion, and under different conditions. In the 

 present volume he extends the results arrived at in his 

 "Theorie generale de la machine a vapeur," and adds to 

 his fundamental equations for the analysis of the trial of 

 a steam engine a sixth term depending upon the condi- 

 tion of the steam in the cylinder at the end of the 

 e.xhaust. 



The natural and artificial aromatic substances at 

 present known are tabulated by Dr. Jaubert. They are 

 arranged in five classes, namely, aromatic alcohols ; 

 aromatic acids ; terpenes ; camphors ; alcohols, aldehydes 

 and terpene acids. A short description is given of the 

 characteristics of each class, and following it are tables 

 showing the commercial name, scientific name, empirical 

 and constitutional formulae, method of preparation, refer- 

 ences to literature, properties and characteristic reactions. 

 The study of these compounds is now the most important 

 branch of organic chemistry, not only from the point of 

 view of pure science, but also on account of their com- 

 mercial value. The book should therefore be found of 

 service to both chemists and pharmacists, as a convenient 

 work of reference. 



Grundzuge der geographisch^norphologischen Methode 

 der Pflanzensystematik. By Dr. R. von Wettstein. 

 Pp. 64. Mit 7 lith. Karten und 4 Abbildungen im text. 

 (Jena: Gustav Fischer, 1898.) 



This suggestive little work, coming as it does from the 

 pen of Prof von Wettstein, will be read with attention 

 by all who are interested in the wider problems of 

 systematic botany. The author contends that a separ- 

 ation of species or sub-species on morphological grounds 

 alone is unsatisfactory, and he reminds his readers that 

 the appreciation of differences by this method must be 

 ultimately a purely subjective one, and that the con- 

 clusions arrived at are liable to be vitiated on several 

 grounds. Von Wettstein pleads for a more general 

 recognition of the geographical areas occupied by species, 

 and considers that a careful study of these will eliminate 

 errjors due to modifications depending on climatical or 

 other physical conditions ; and it is well known how 

 efficient these are in producing races which, though 

 retaining a general resemblance to a common ancestor, 

 may yet be greatly dissimilar amongst themselves. 



He applies his methods to a study of the Endotricha- 

 series of Gentians, and thus comes to reduce the twenty- 

 two species to six ground-forms or genuine species. 



He further discusses some of the Euphrasias, and 

 arrives at a corresponding result. It may, however, be 

 urged that this method also is open to objection, and 

 [hat more is to be got out of the study of species by 

 experimental cultivation — an arduous task, but one which 

 will perhaps yield more fruitful results than even the 

 application of the geographical-morphological method. 



Dreams of a Spirit- Seer^ illustrated by Dreams of Meta- 

 physics. By Immanuel Kant. Translated by E. F. 

 Goervvitz, and edited with an introduction and notes 

 by Frank Sewall. Pp. xiv -t- 162. (London: Swan, 

 Sonnenschein and Co., Ltd., 1900.) 

 The chief object in publishing this translation of Kant's 

 " Traiime," which first appeared in 1766, is to show the 

 relation between the philosophy of Kant and the teach- 

 ings of Swedenborg. Students of metaphysics and 

 psychology will appreciate this '>aid to a study of Kant's 

 philosophical development. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. '\ 



On the Process of Dyeing with Woad Alone. 



In my paper in Nature (February i, 1900, p. 331) on the 

 blue colour in woad, no account is given of the method by which 

 prepared woad can be used for dyeing wool blue. Some of my 

 friends have suggested that the above-named communication 

 was, in consequence, like the play of Hamlet with the Prince of 

 Denmark left out. The request for information then made as to 

 the jnodus operandi of the mediaeval dyers who used woad and 

 woad alone for dyeing blue has up to the present yielded no 

 response. 



There exists a tendency to believe that by long-continued 

 cultivation the woad now grown and prepared in this country 

 has lost its power of dyeing blue, and is only of use in setting 

 up fermentation in the indigo vat. It is, however, very im- 

 probable that a plant like Isatis tinctoria should entirely lose so 

 characteristic a property as that of indigo-formation. It was, 

 however, possible that some variation in the details of its manu- 

 facture might have had this effect. That fresh woad still can be 

 made to yield indigo was shown, and the process of extracting it 

 given in detail, in the paper above referred to. 



Prepared woad is a dark brown, earthy-looking paste having 

 an ammoniacal odour, yielding a yellowish-brown solution to 

 water, and looking as unlikely a source of a blue dye as could 



NO. 1589, VOL. 61] 



