646 



SCIENCE. 



[N. P. Vol. IX. No. 224. 



tains to the printer's art, is more satisfactory 

 than perhaps in any modern text-book of sci- 

 ence, and the more one investigates the book 

 itself the more one is convinced that the au- 

 thors have successfully accomplished their pur- 

 poses. 



The subject-matter is arranged in the follow- 

 ing order : Mechanics, Heat, Electricity, Sound 

 and Light. The scope of the book is rather 

 wider than would allow its use in most colleges 

 or schools, including, as it does, such points as 

 radius of gyration, compound pendulums, Car- 

 not's cycle, Thomson and Joule's experiment, 

 entropy, virial, osmotic pressure, thermo-elec- 

 tricity, theory of alternating currents, impe- 

 dance and so on, electric waves, eflaciency of 

 optical instruments, theories of color sensation, 

 and wave surfaces of uniaxal and biaxal crys- 

 tals. A knowledge of trigonometry and the 

 elements of analytical geometry are presup- 

 posed for the study of the book, but no previous 

 knowledge of physics is expected. 



Each of the main subjects of Physics is dis- 

 cussed with considerable fulness and is illus- 

 trated by many natural phenomena and by 

 many mechanisms and devices in common use. 

 This is particularly true in the subjects of Me- 

 chanics and Electricity. One knows before 

 one looks that there will be a most satisfactory 

 explanation and discussion of optical instru- 

 ments. In fact, all the chapters on Light are 

 of marked excellence. 



It should be particularly noted that special 

 attention is paid throughout the book to the de- 

 scription of the various instruments used in 

 phj'sical measurements. The chapters on music, 

 musical instruments and color-sensation are 

 admirable. The book closes with an excellent 

 index. 



One may think that occasionally there is 

 want of balance in the amount of space given 

 various subjects and in the arrangement of 

 these subjects. For instance, the space given 

 the ' conservation of momentum ' is only about 

 half a page, whereas that given the centrif- 

 ugal drier and the centrifugal cream sep- 

 arator amounts to nearly four pages. The 

 discussion of measurement of matter and of 

 the concept of force is most briefly stated. 

 It may be said, however, that in a text-book of 



this character, where the purpose is not to 

 acquaint students with the fundamental princi- 

 ples of Physics and with their logical develop- 

 ment, but rather to give them a knowledge ex- 

 tending over wide fields of the phenomena of 

 Nature and to correlate these in groups, such 

 criticism as this is not applicable. 



If one speaks of certain questions which do 

 not seem to be treated as well as they might be, 

 it is not from any wish to detract from the high 

 merit of the book, but rather to call the at- 

 tention of teachers who may use the book to 

 certain points concerning which questions might 

 be raised. In particular, it is doubtful if the 

 chapter on Thermometry or on Calorimetry 

 could be regarded as satisfactory by a class. It 

 is hardly fair in defining a scale of temperature 

 to use, as is done on page 165, the formula for 

 the law of gases, and then to state, as is done 

 on page 179, that " Experiment has shown that 

 in the case of a gas under constant pressure not 

 only is the expansion strictly proportional to 

 the increase of temperature, but that all gases 

 have sensibly the same coefficient." This 

 seems to be using a quantity to define temjier- 

 ature and then to make use of the definition in 

 stating a law. 



Again, the words 'definite quantity of heat' 

 are used in what may be considered an indefi- 

 nite manner. On page 251 the authors use 

 the following words: "The now universally 

 adopted theory that heat is the kinetic energy 

 due to the irregular motion of the molecules of 

 a body " — a statement which is not altogether 

 justifiable. It is possible to speak of the energy 

 of a body and to consider it as partly kinetic 

 and partly potential, using the latter name 

 simply to include all energy that is not, strictly 

 e a king, kinetic from our present knowledge ; 

 and it is possible also to say by way of defini- 

 tion that we will call the kinetic energy of the 

 parts of the body by the name 'Heat.' This, 

 however, is quite a different matter from saying 

 that all the heat-effects are manifestations of 

 kinetic energy, or from using the word ' Heat ' 

 in the sense of something that is ' applied ' 

 to a body, which is the sense most commonly 

 used by the authors. 



It is to be regretted that such phrases as 

 ' molecular attractions of the particles of a solid 



