July 20, 1882] 



NATURE 



267 



German students, and its introduction is to be regretted, 

 as it is likely to deter scientific students from taking up 

 crystallography. 



In the special part devoted to the several systems, Dr. 

 Liebisch proceeds from the principle of symmetry, in 

 which, however, he defines his systems by means of axes 

 and a centre of symmetry, instead of by planes of sym- 

 metry. This is done with a view to include the hemi- 

 hedral forms in the same definition as the holohedral 

 ones, and to obviate the difficulty arising from the hemi- 

 hedral forms being excluded when the system is defined 

 by means of planes of symmetry. One doubts, however, 

 whether the advantage gained is sufficient to compensate 

 for the loss of simplicity. Dr. Liebisch has made a 

 curious slip in his definition of symmetry, being appa- 

 rently carried away by his love of generalisation. He 

 shows that the internal and external bisectors of an angle 

 divide symmetrically the spaces portioned out by this 

 angle, and that the four lines form a harmonic pencil. 

 He then generalises this relation, and leads one to suppose 

 that symmetry always exists when a pencil is harmonic. 

 The fallacy of this is clear when one considers that the 

 planes 100, 101, 001, and 101 in the oblique system would 

 thus show symmetry, since they are harmonic conjugates. 

 Dr. Liebisch points out that the indices of the planes in a 

 form can be deduced from those of one of the planes when 

 the symmetry is given. The deduction though simple is 

 sufficiently difficult, and it would have been better to have 

 given it fully. Another omission is found in the problem of 

 isogonal zones, i.e. the determination of the possible angles 

 between planes of symmetry. The solution is carried out 

 so far as to show that the angles must have the squares 

 of the cosines rational, and then the special values are 

 given. No attempt is made to show that these are all 

 the possible cases. It is not difficult to find all the sub- 

 multiples of 180 which satisfy the condition, and the 

 complete solution has long since been worked out by 

 Axel Gadolin and Prof. Maskelyne. 



The author is remarkably well read in the literature of 

 crystallography, and has done much to compress the 

 valuable portion of this literature into the space of a 

 comparatively small volume. The book is certainly not 

 suited as a text-book for students who are beginning 

 crystallography ; and its methods of solution of crystals 

 are not the simplest in practical work. For advanced 

 students, who wish to regard their subject from different 

 points of view, it will be a suggestive book ; and, not- 

 withstanding its omissions, will very greatly assist them, 

 both by its own statements and solutions of the problems 

 of crystallography, but also by its careful references to 

 the literature of the subject. It is well printed, and has 

 a large number of excellent woodcuts. 



OUR BOOK SHELF 



A Dictionary of Popular Names of the Plants which 



furnish the Natural and Acquired Wants of Man. in 



all Matters of Domestic and General Economy; their 



History, Products, and Uses. By John Smith, A.L.S. 



(London : Macmillan and Co., 1882.) 



The lengthy and somewhat incoherent title cited above 



is less expressive of the aim of this volume than the 



abbreviated form which appears upon its cover— viz. 



"Dictionary of Economic Plants." Mr. Smith, the 



veteran ex-curator of Kew Gardens, has brought together 

 a great deal of information with regard to economic 

 plants ; and his facts, although sometimes open to criti- 

 cism if examined in detail, are in the main trustworthy. 

 It is not always easy, however, to reconcile the contents 

 of the volume with its title ; interesting as are such plants 

 as the "side-saddle flower" (Sarracenia), "telegraph 

 plant" {Desmodium gyrans), broom rape, wallflower, 

 Virginian creeper, mignonette, and the like, they can 

 hardly be regarded as supplying either the "natural " or 

 the "acquired wants of man." We have tested the work 

 somewhat carefully, and have in almost every instance 

 found the name we were seeking ; and we can therefore 

 say that this Dictionary, although not perhaps particularly 

 needed, may be usefully referred to by those interested in 

 economic botany. 



Induction. By Willoughby Smith. 17 pp. (London : 



Hayman Brothers and Lilly, 1882.) 

 In this work Mr. Willoughby Smith gives an account of 

 some curious and interesting experiments on magneto- 

 electric induction as revealed by the Bell telephone. In 

 one of these experiments an intermittent current was sent 

 through a flat spiral coil of wire 36 inches in diameter con- 

 taining 12:0 yards of wire in Soo turns. When an ordinary 

 Bell telephone, unconnected with the circuit, is held within 

 a few feet of this, spiral sounds are heard in it, even if the 

 coil of the telephone be removed, leaving only the iron 

 tympanum and the magnet. Mr. Smith however appears to 

 regard this effect as something not explainable on the 

 ordinary laws of electrical action, and he applies a new 

 term, "specific inductive resistance," to the power of a 

 medium to stop such inductive action. He thus intro- 

 duces a confusion between two conditions in the case. 

 That such induction should be propagated depends upon 

 the coefficient of magnetic induction, and also depends 

 upon the damping of induction by the setting up of 

 currents in an interposed sheet of metal. Both these 

 causes are perfectly well known. It is a pity that an 

 able experimenter commits himself to crude ideas of this 

 kind. There are several good plates of figures added. 



LETTERS TO THE EDITOR 

 [ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [ The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to ensure the appearance even 

 of communications containing interesting and novel facts.} 



The Mount Pisgah (U.S.) Stone Carvings 



Permit me to make the following remarks on Dr. Rau's 



letter in Nature, vol. xxvi. p. 243. I ho] e shortly to lay 



before your readers a statement of the facts relative to the 



objects under discussion. 



At Prof. Baird's request I met him and Dr. Rau at Washing- 

 ton with the carvings and photographs I now have in Europe. 

 These were looked at by Dr. Rau, and he now states as die result 

 that he is "enabled to express an opinion concerning them," 

 and that "they neither show the characteristics of the stone 

 sculptures discovered in the mounds, nor do they resemble the 

 well-known specimens of modern Indian art." 



Now if Dr. Rau had compared certain of these objects with 

 some of those found by Squier and Davis in the Scioto mounds, 

 he might probably have "discovered," as I did some time ago, 

 and others have observed since, some resemblance in them. 

 Moreover, there are objects in the collection which may hive 

 been, and no doubt were, made by Indians. A striking illustra- 

 tion appears in a very rudely incised stone — photographs of 

 which Dr. Rau saw ; an Indian is represented with feathers in 

 his head and a flint-lock gun in his hand. But, notwithstanding 

 the occurrence of this and a few other similarly treated objects, 

 the majority of these carvings do not "resemble the well-known 

 specimens of modern Indian art." In the representations of the 



