September 29, 1911] 



SCIENCE 



409 



biology are subdivisions of tbe broader science 

 of cbemistry." Should it not be possible to 

 find a core of this work which is essential 

 chemistry and teach that? 



The physics people have met the challenge 

 concerning boundaries and disputed territory 

 courageously. It is not long since I heard a 

 university professor begin a lecture on phys- 

 ics somewhat in this way : " Physics is the 

 science of matter and energy. This iield is so 

 large that it is customary at present to break 

 off the physics of the molecule and its reac- 

 tions and call it chemistry. Also to put to 

 one side the physics of the heavenly bodies 

 and call this part astronomy," etc. So these 

 two subjects, physics and chemistry, have been 

 mutually devouring each other, like two Kil- 

 kenny cats, lo these many years. It seems to 

 have been good for them, however, for both 

 have grown to be lusty fellows. The only diffi- 

 culty seems to be to determine which is which. 

 Suppose we give up trying, call the amalga- 

 mated science what you like, and frankly 

 make a two-years course in this science, 

 with the topics arranged in logical order, as 

 an elementary book for high schools. This 

 would dispose of the not very important but 

 still much discussed question whether chem- 

 istry should come in the eleventh or the 

 twelfth year, as well as the far more impor- 

 tant matter of extensive duplication. At first 

 sight it might seem desirable to repeat a large 

 amount of physics in the chemistry classes, 

 especially as this part is in general very im- 

 portant, but a moment's thought will convince 

 any one — ^not already convinced by experience 

 — that this is not likely to be true. The work 

 presses; the class will meet these subjects else- 

 where; nobody is responsible for a full pre- 

 sentation of them; and so the few ideas most 

 essential to further progress are made to 

 suffice. There is no one to apply the excellent 

 homestead law — one must not only stake out a 

 field but occupy and do some work upon it. 



If a two-years' unitary course in physical 

 science can not be secured, some competent 

 authority — say a joint committee of the chem- 

 ical and physical societies of America — might 



be asked to say what shall be taught as chem- 

 istry and what as physics. For instance, 

 where shall the modern doctrine of solutions 

 be taught? How much of combustion, of 

 electrolysis, of the action of a primary bat- 

 tery, is chemistry and how much physics? 

 E. A. Strong 



SCIENTIFIC BOOKS 

 Physical Optics. By Egbert W. Wood, 

 LL.D., Professor of Experimental Physics 

 in Johns Hopkins University. Second Edi- 

 tion. New York, The Macmillan Company. 

 1911. Pp. xvi + 705. Price $5.25 net. 

 To those who are acquainted with the 

 earlier edition of Wood's " Physical Optics " 

 it will be high and just praise of the second 

 edition merely to say that it is vastly superior 

 to the first. The new material added to the 

 former discussion — roughly, fifty per cent. — 

 illustrates the tremendous recent development 

 of physical optics; and the manner in which 

 all this work is described continues to illus- 

 trate the extraordinary clarity and precision 

 with which intricate matters may be set forth, 

 in a non-mathematical way, by a man who 

 really and profoundly understands his subject. 

 Of the various additions and improvements, 

 perhaps the following will serve to character- 

 ize the whole: 



The first three chapters have not been much 

 altered, although they do contain some new 

 material, such as the work of Galitzin and 

 Wilip on Doppler's principle, Pfund's mercury 

 arc, etc. 



A very characteristic addition finds place 

 in the fourth chapter, the one dealing with 

 refraction, where a series of photographs 

 taken with a lens immersed in water — a " fish- 

 eye camera" — has been inserted. These give 

 a concreteness and directness to the treatment 

 of the critical angle which could hardly be ob- 

 tained in any other manner. 



Chapter V., on dispersion, shows few 

 changes, but is enriched by a plate showing 

 Julius's remarkable series of photographs of 

 the " D " lines, under various physical cir- 

 cumstances. 



The value of the chapter on diffraction is 



