6l2 



NA rURE 



[October 28, 1897 



cells are treated of in § 243, but not, we think, quite 

 successfully. It is stated, among other things, " that 

 there is a slight difference [of potential] at the junction of 

 the copper and the zinc," and it is implied that the charge 

 in potential in passing from the liquid to the zinc is 

 considerable. "These facts, it is said, may be proved by 

 direct ex periment." While in all probability these state- 

 ments would be found true if we could measure the 

 actual potential of the zinc, the copper and the acid, 

 direct experiments, measuring as they do the potential in 

 the air near the zinc and copper, seem to show us that 

 these differ in potential considerably. 



Book V. deals with light, and bases the explanations 

 entirely on the wave theory. 



There is much to be said for such a treatment ; still 

 some of the proofs given necessarily want in rigidity — 

 eg. that in § 306, on the law of reflection — and the 

 clearness of conception acquired by the student who 

 makes a careful study by graphical methods of the 

 phenomena afforded by lenses and mirrors is a great 

 gain to him. 



The book is clearly printed and admirably got up ; 

 the diagrams are good ; the plate of spectra in black and 

 white, facing p. 264, is a marked improvement on many 

 of the chromolithographed plates we have seen. 



OUR BOOK SHELF. 



A Detailed Course of Qualitative Chemical Analysis of 

 Inorganic Substances., with Explanatory Notes. By 

 Arthur A. Noyes, Ph.D. Pp. 89. Third edition. 

 (New York : The Macmillan Company. London : 

 Macmillan and Co., Ltd., 1897.) 

 The present work arose out of the difificulty experienced 

 by the author in attempting to give a thorough course 

 of qualitative analysis in limited time to large classes of 

 students. Of course in a work dealing with so hackneyed 

 a subject anything new must be looked for in the 

 arrangement of the material. It is a common practice to 

 preface the actual analytical separations by a course of 

 test-tube reactions with each metal and acid, with 

 the object of combining a course of systematic inorganic 

 chemistry with the study of analysis. The author 

 prefers to keep the two separate, thinking that the former 

 is better taught by a course of inorganic preparations 

 than by the test-tube reactions, which mostly involve 

 mere questions of solubility. The present course ac- 

 cordingly plunges at once into the separations of the 

 metals, passing on to the wet tests for acids, and 

 concluding with dry tests and an excellent chapter on 

 the preliminary preparation of substances for analysis. 

 The book is intended to be used in the laboratory, and to 

 be accompanied by lectures on, and demonstrations of, 

 the analytical processes. When employed in this way 

 it is thoroughly to be commended. Minute directions 

 are given for carrying out each operation, followed by 

 notes explaining the reason of everything which is done, 

 and the apparently anomalous results which may arise 

 from the neglect of the precautions specified, or from 

 other causes. These notes form a peculiarly excellent 

 feature of the book, and reveal the hand of the ex- 

 perienced teacher. The section on the tests for acids 

 is, perhaps, the least satisfactory, the tests selected 

 being, in the writers opinion, not invariably the best 

 available. 



The printing, paper, and binding are uncommonly 

 good, and a useful index is provided. 



NO. 1 46 I, VOL. 56] 



Physikalische C/ieinie fiir A nf anger. By Dr. C. M. 

 van Deventer ; with a preface by Prof J. H. van 

 't Hoff. Pp. 167. (Amsterdam : S. L. van Looy. 

 Leipzig: W. Engelmann, 1897.) 



Prof, van 't Hoff says, in his preface, that he had 

 experienced, in his lectures to medical students, the 

 want of a text-book dealing with the general laws of 

 chemistry in an elementary way, a want which was 

 supplied by Dr. van Deventer's book. The book begins 

 with definitions of terms, and then goes on to the laws 

 of chemical combination, the laws regulating the be- 

 haviour of gases, Avogadro's hypothesis, atomic and 

 molecular weights. The fourth chapter deals with the 

 specific heats of elements and compounds, and contains 

 an excellent resume' of the more important results of 

 thermo-chemistry, concluding with the laws of mass 

 action and some pages on distillation. The last three 

 chapters deal briefly with the theory of solutions, spectro- 

 scopy and photo-chemical action, and the periodic law. 

 Although it might be objected that the discussion of 

 the asymmetric carbon atom on p. 40 is somewhat 

 beyond first-year students, that too much space is devoted 

 to the erroneous principle of maximum work, and too 

 little to the hypothesis of electrolytic dissociation, which 

 is of such great interest in connection with the qualitative 

 analytical work which forms a considerable portion of 

 the laboratory practice of elementary students, yet these 

 are matters on which different teachers would entertain 

 different opinions, and on the whole it must be said that 

 the work is thoroughly well done and suited to the 

 purpose for which it is intended. 



Brotnide Enlargements., and How to Make them. The 

 Popular Photographic Series, No. 13. By J. Pike. 

 Pp. 64. (London : Percy Lund, Humphries, and Co., 

 1897.) 

 There are many of us who delight in the use of hand 

 cameras, but who find those of larger size too cumber- 

 some and unwieldly to carry about. With the former 

 pictures may be obtained without those numerous pre- 

 liminaries which must be gone through every time a 

 picture is required, such as putting up the tripod, setting 

 up the camera, &c., but their size necessitates that 

 the pictures must be rather small. These latter can, 

 however, be enlarged when required, and it is with this 

 special subject that the present little book deals. The 

 process is quite simple, as will be gathered from the 

 sixty-four pages in which the author brings together all 

 information that the operator can require. Not only 

 is the actual method of making bromide enlargements 

 described, but useful hints will be found on constructing 

 one's own apparatus, the different sources of light avail- 

 able, screens, skies and sky printing, &c. The book 

 forms an interesting addition to the popular photographic 

 series, and it should be widely read. 



The Machinery of the Universe : Mechanical Conceptions 

 of Physical Phejtomena. By Prof A. E. Dolbear, A.B., 

 Ph.D. Pp. vi 4- 122. (London: Society for Promoting 

 Christian Knowledge, 1897.) 



In December 1895, Prof. Dolbear delivered before the 

 Franklin Institute of Philadelphia a lecture on mechan- 

 ical conceptions of electrical phenomena, and the sub- 

 stance of it was published in Nature a year ago (vol. 

 Iv. p. 65). The lecture has been enlarged by the ad- 

 dition of a section in which the properties of matter and 

 the ether are compared, and it now forms one of the 

 "Romance of Science" series of the Society for Pro- 

 moting Christian Knowledge. The aim of Prof. Dolbear 

 is to show that the mechanical antecedents of physical 

 phenomena are sufficient to explain the phenomena 

 without assuming the existence of other factors. 



