5° 



NA TURE 



[May 15, 1884 



who approach the subject freshly, modern ideas come to 

 the front. The question of viscosity of solids and liquids 

 comes prominently forward. The views of Crookes on 

 the "radiant" condition of highly attenuated gases are 

 discussed, and so is also the connection between the 

 liquid and gaseous states. With respect to the alleged 

 continuity between these states, the author does not seem 

 to have quite made up his mind; for though he'quotes 

 with approval the proof given by Ramsay, that the so- 

 called critical point is not necessarily a phenomenon of 

 continuity at all, but simply a certain condition of things 

 in which the liquid and its vapour mix, because they have 

 arrived at equal density and cannot keep separate, he 

 seems also to lean to the other view, apparently relying 

 on an unconfirmed observation by Hannay on the solu- 

 bility of a solid in a gas. The vortex theory of atoms 

 and the existence of the ether are mentioned in this 

 chapter. There is a capital section on elasticity, and 

 another on liquids, in which the molecular pheno- 

 mena of liquid cohesion and surface-tension are given 

 due weight, as are also sundry matters concerning the 

 kinetics of liquids, often omitted from such text-books. 

 A short chapter on Gases is introduced, and then follows 

 one on Heat. Just fifty-one pages are given to this entire 

 subject ; but in those fifty-one pages an enormous amount 

 of useful matter is comprised. There is not a superfluous 

 line or even word. This extraordinary success— for the 

 thing is most successfully done— is largely due to the 

 author's fundamental method of stilting from the energy 

 doctrine. The chapter on Heat opens with the first law 

 of thermodynamics, and states it thus : " Heat, being a 

 form of energy, can be measured in ergs." The rest of 

 the subject is developed in a misterly way : though pro- 

 bably the student who has read nothing previously in this 

 branch will find it tough. The paragraph on " the six 

 thermal opacities" is very suggestive, and needs clear 

 thinking to follow it. The author adheres, not quite 

 wisely, we think, to the practice of taking as the defini- 

 tion of the calorie or heat-unit, the kilogramme -water- 

 degree unit instead of the gramme-water-degree unit. 

 This is the only case in which the author does not accept 

 the C.G.S. system. Is there any adequate reason why 

 he should not follow the more modern custom and adopt 

 the calorie mineure instead of the calorie majeure ? The 

 chapter on Sound is also well written ; and, for the first 

 time, so far as we are aware, we have the notation of the 

 tonic" sol-fa system introduced along with staff notation 

 into the discussions of pitch and temperament. 



The chapter which succeeds is enough to take away one' s 

 breath. Were this a text-book of the stereotyped acade- 

 mic style, one would know exactly what to expect. After 

 Sound', Light : a chat on the velocity of light ; the old 

 familiar gray-headed problems of reflection and refrac- 

 tion ; a glance at the rainbow and at telescopes and 

 microscopes ; and, to wind up, a couple of pages on the 

 spectrum— with the inevitable chromolithographed chart 

 —and two more on polarisation. But this is not the 

 method of our author. He heads his chapter, ; - Ether- 

 Waves.'' and after a little preliminary clearing away he 

 launches into radiation and introduces notions on wave- 

 length, heating effects, colour, and on exchange of radia- 

 tions. Prevost's law and Stokes' law lead direct to the 

 analysis of radiations in the spectrum, and to the evj. 



dence afforded in the spectrum of the phenomena of 

 transmission, reflection, and absorption. The propaga- 

 tion of waves through the ether next comes up, involving 

 the questions of plane and circular polarisation, and then, 

 after all this, — shades of the immortal Potter and of the 

 revered Todhunter ! — come reflection and refraction of 

 light, minors, prisms, and lenses! This is indeed a 

 bouleversementoi the time-honoured custom of giving all 

 attention to geometrical optics, leaving physical optics to 

 take its chance at the fag end. Yet we are persuaded that 

 the method is essentially right. It is to be regretted, 

 however, that the author does not, with all his improve- 

 ments, adopt Gauss's treatment of lens problems. Perhaps 

 this is solely for want of space ; the sin, if it be one, is 

 one of omission only. Separate sections on interference, 

 double refraction, optical instruments, and rotatory 

 polarisation are given. The instruments are briefly but 

 satisfactorily discussed ; the ophthalmoscope and stereo- 

 scope receiving due attention. The last and longest 

 chapter in the book is devoted to Electricity and Mag- 

 netism. This chapter, though abounding in good points, 

 is to our mind the least successful of the whole ; it will 

 not satisfy electricians, though it may, and will, give to 

 medical students a very good and thorough insight into 

 the phenomena and laws of electricity. A very useful 

 bibliography of works on physics for further reading 

 closes the book. 



One further point strikes us in reviewing the book as a 

 whole— the excellence of the examples chosen to illustrate 

 the problems and remarks. Particularly to medical 

 students will this feature recommend itself. Levers and 

 moments of forces are illustrated at p. 151 by a long list 

 of articulations in the human skeleton. The references 

 on p. i.U to the action of the biceps and deltoid muscles, 

 on p. 13S to Rosapelly's researches, on p. 143 to ansemic 

 disorders, on pp. 252-55 to the relations of the physical 

 processes of osmose and diffusion to the tissues of the 

 body in relation to juices, foods, alkaloids, and to serpent- 

 poisons, will be recognised as giving a distinctive charac- 

 ter to the work. 



Such criticisms as it remains for us to pass are directed 

 solely to a few points in which the author will do well to 

 modify the work when it shall attain— as it doubtless will 

 —to a second issue. In the section on the rainbow the 

 secondary and tertian-, &c, bows due to multiple in- 

 ternal reflection are apparently confused with the super- 

 numerary bows due to interference. On p. 35 the 

 " watt " is wrongly defined as a unit of work, and equal 

 to 10" ergs, whereas it is not a unit of " work " at all, but 

 a unit of " activity," and is equal to 10" ergs per second. 

 The matter recurs on p. 575, but is not there much mended. 

 The author uses the letters " E.M.D.P.," meaning there® 

 " electromotive difference of potential," for that which is j 

 more commonly denominated " electromotive force," and i 

 abbreviated into " E.M.F." We cannot think the change, 

 well advised. What would the author do if he came to, 

 discuss the formula? of a dynamo, in which the induced, 

 electromotive force is a very different quantity from rjel 

 difference of potential between the terminals ? Would he 

 write both "E.M.D.P." ? Again, on p. 625, the author, 

 uses "utility" for the quantity commonly called the,, 

 "efficiency " of an electric motor. This is in itself not. 

 perhaps a bad exchange of terms. But the author goes 



