May 15, 1884 



NA TURE 



5' 



>n to misapply the very same word and to use it in the 

 ense of "activity," saying in effect that (by Jacobi's law) 

 he "utility" is a maximum when the reaction of the 

 notor reduces the supply-current to one-half. The dia- 

 ram intended to represent Hall's experiment on p. 62S 

 3 quite wrong. The statement on p. 503 that the velocity 

 f light is greater in metals than in air is incorrect : the 

 efractive index is greater, therefore the velocity less. 

 'he author has most wisely abandoned the use of that 

 lost misleading of terms, vapour-tension, and substitutes 

 lerefor simply pressure. This is well ; but the reform 

 lust go further, and should have gone further at the 

 ands of so worthy a pupil of the Scottish school of 

 hysical precision. A reference to the index shows 

 pparently that the author uses the word "pressure " cm - 

 ■ctly and consistently in the sense of force per unit area. 

 :" this were so, it would be excellent. Unfortunately 

 le text of the treatise is not always consistent. On p. 

 ■,2 the author talks of applying a " pressure " to a lever, 

 here he does not mean so many dynes per square centi- 

 letre, but where he means simply a "force,"— a push, 

 f course this confusion of language is pardonable : it 

 ins riot throughout every Cambridge text-book of me- 

 lanics from Todhunter to Garnett. We had hoped 

 itter things here. Again on p. 154 comes the following 

 lestion:— "A nutcracker 6 inches long has a nut in it 

 1 inch from the hinge : the hand exerts a pressure of 

 lbs. : what is the stress on the hinge ? " Answer : " The 

 ress on the hinge is the weight of 24 lbs." In the first place 

 e word "stress " is wholly misapplied ; for a stress is not a 

 rce, but a force divided by the area on which it is 

 iphed : and in the second the word " pressure " is 

 :ually misapplied, because what is meant is that the 

 ind applies a " force " equal to the weight of four pounds. 



like manner the author's general precision of lan- 

 lage would lead to the expectation that he would not 

 isapply that unhappy word "tension." Referring to the 

 dex it appears that he uses the word tension in four 

 fferent senses. He speaks of "surface-tension" of a 

 uid : which is excusable if the words are connected by 



indissoluble hyphen. He speaks of voltaic cells being 

 upled in "tension," where he means united in series. 

 e speaks (p. 522) of atmospheric pressure in an electri- 

 d soap-bubble being resisted by " an electric self-repul- 

 m or tension over the surface" (as if self-repulsion were 

 pulling instead of a pushing force !) ; and lastly, he 

 saks of the "tension" of a string (p. 142) when he 

 ;ans the pull, not the stress of so many dynes per 

 •lare centimetre. He is no worse, however, than the 

 ijority of writers on the subject. The average Cam- 

 dge text-book teems with similar instances, where 

 >blem after problem is set to " find the tension in a 

 >e," without the necessary data as to area of cross- 

 tion in the rope being given. There is one book on 

 fsics, now happily almost extinct, in which the word 

 sion is used in eight different significations ! 

 -astly, we must congratulate Mr. Daniell on having 

 bodied the latest results of contemporary research in 

 work. The ordinary text-book is not seldom ten or 

 :en years behind in its data, in some cases more, 

 re, however, we find, absorbed into the fibre of the 

 >k, the most recent matter, such as the researches of 

 :d Rayleigh on the unit of resistance, of Quincke and 



of Worthington on capillary phenomena, of Guebhard on 

 electro-chemical figures, of Crookes on radiation and 

 "radiant matter," of O. E. Meyer on viscosity, of A. M. 

 Mayer on the analysis of sounds, of Rosenthal on anim ij 

 heat, of Vierordt and of Chauveau on blood-pressure, ot 

 Wintrich on the use of resonators in auscultation, and of 

 Abney and of Langley on dark radiation. A text-book so 

 furnished forth is doubly welcome. S. P. T. 



RECENT CHEMISTRY 

 Experimental Proofs of Chemical Theory for Beginner*. 



By Prof. Ramsay. (London : Macmillan, 1884.) 

 The Discovery of the Periodic Law, one! on Relation* 

 among the Atomic Heights. By John A. R Newlands. 

 (London: Spon, 1SS4.) 

 Chemical Analysis as applied to the Examination of Phar- 

 maceutical Chemicals. By Messrs. Hoffmann and 

 Power. Third Edition. (London : Churchill, 18S4.) 

 Chemical Analysis, for Schools and Science Classes. By 



A. H. Scott- White. (London: Laurie, 1884.) 

 Facts Around Us. By C. Llovd Morgan. (London - 



Stanford, 1884.) 

 Science of Food. A Text-book specially adapted for 

 those who are preparing for the Government Examina- 

 tions in Domestic Economy. By L. M. C. (London : 

 George Bell and Sons, 1884.) 

 An Outline of Qualitative Analysis for Beginners. By 



J. T. Stoddard. (Massachusetts, 1883.) 

 'T'HERE is not the least doubt that in English labora- 

 -•- tories theory does not occupy a prominent position. 

 Prof. Ramsay is to be complimented on this very small 

 book, which is certainly a valuable attempt to put chemi- 

 cal theory on a practical basis. It consists of a series of 

 exercises on the measurement of temperature, pressure, 

 and weight in connection with gases, &c, and contains 

 very valuable directions and instructions in the manner 

 of reading thermometers and barometers, and represent- 

 ing changes by curves, and also in the graduation of 

 thermometers and other instruments in common use in 

 the chemical laboratory, a work which should not be 

 relegated entirely to a physical laboratory. The work is 

 divided into twelve chapters, in all of which we have very 

 excellent practical exercises on what is commonly known 

 as chemical theories, that is, the sensity of gases, the law 

 of Gay Lussac and Avogadro, on quantivalence, specific 

 heat, and the equivalents of metals, and a short chapter 

 summarising Newlands' work on the periodic law of the 

 elements. We can strongly commend this little book 

 to all students in chemical laboratories. 



Mr. Newland's little book, as the author says in his 

 preface, contains an exact reprint of all the papers on 

 relations among the atomic weights and on the periodic 

 law written by himself and printed in the Chemical News 

 during the last twenty years. In its present form it is a 

 desirable addition to our literature, and should bring Mr. 

 Newlands' very valuable work into its proper position. 



Messrs. Hoffmann and Power's very elegant work is 

 evidently not adapted to an ordinary chemical labora- 

 tory. As the authors state, it has been prepared for the 

 pharmacist and dispensing practitioner of medicine, for 

 the purpose of enabling him to test chemicals and drugs 

 used in pharmacy. The arrangement of the work is 



