Decbmbee 18, 1908] 



SCIENCE 



889 



sibly, a full presentation of simple harmonic 

 motion might be appropriate, since all waves, 

 transverse or longitudinal, which result in 

 sound are of that form of motion, but it could 

 hardly be necessary to go into any considerable 

 discussion of elasticity or the determination of 

 elastic constants. It should be sufficient, it 

 would seem, to point out that in accordance 

 with Hooka's law all vibrations due to elas- 

 ticity are simple harmonic motions. In 

 America, at least, a student capable of read- 

 ing a work like this intelligently would very 

 probably be so far familiar with the principles 

 of elasticity as to make chapter III. super- 

 fluous, and the like would be true regarding 

 some other portions that are not obviously of 

 an acoustic nature. Even if their connection 

 with acoustics is ultimately fundamental, it 

 is so remote as to suggest comparison with the 

 works of a watch which have nothing to do 

 with the case. Their presence, however, is not 

 a serious fault if it secures better treatment of 

 other parts that could not be omitted. It is 

 a question whether simple harmonic motion 

 in connection with sound is not overdone. It 

 is true that elastic vibrations are simple har- 

 monic motions, but so far as sound is con- 

 cerned its reception by or transmission to the 

 ear is always due to longitudinal vibration, 

 and the intricate composition of transverse 

 vibrations helps very little in interpreting the 

 superposition or interference of longitudinal 

 waves in the medium through which the sound 

 is transmitted. Still, the phonograph and the 

 telephone have of necessity forced the study of 

 acoustics along the line of vibrating plates. 

 It is interesting to note how the very delicate 

 points in acoustics are best appreciated by see- 

 ing instead of hearing. 



The last chapter, devoted to recorders and 

 reproducers, is most interesting and important, 

 although some of it goes pretty far afield for 

 sound. A good instance is given of rhythm 

 resulting from sound vibrations and, without 

 being itself sound, transmitted electrically as 

 rhythm and perceived by dipping fingers into 

 a conducting liquid. This may illustrate the 

 vibrations of a plate as a source of sound, but 

 they are neither transmitted nor perceived as 

 sound at all, there being no evidence of any 



material vibration in the transmitting media 

 or in the organ of perception. Of course 

 this is very different from telephonic repro- 

 duction, where there is distinctly a sounding 

 disk at the receiving as well as at the sending 

 terminal. This chapter serves to show how 

 greatly the domain of acoustics has widened 

 since the earlier work of Donkin and Helm- 

 holtz, and it also points out how the theory of 

 sound is connected with that of electricity 

 through wave motion. The value of the 

 chapter is heightened by the original work of 

 the author upon electric oscillations. 



We notice the introduction of the term 

 sound-rays. Although this is unusual, the use 

 of the term ray to designate a normal to a 

 wave front is becoming so common in text- 

 books as to justify it in connection with 

 sound, even though the conception of a ma- 

 terial ray of sound has never had any favor. 



In enumerating several forms of sensitive 

 flames the Govi-Barry flame, which is so easy 

 to produce and so wide in its range of sen- 

 sibility might well have been included. 



A few errors have escaped the proof-reader, 

 but probably not more than are to be expected 

 in a first edition. Such are the omission of 

 an exponent after equation (1) on page 225, 

 and an uncompleted sentence at the top of 

 page 371. But when the few points have been 

 mentioned to which exception might be taken, 

 there remain so many more to be commended 

 that the balance is greatly in favor of the 

 work. The admirable choice and distribution 

 of experiments, the masterly character of the 

 discussions, the ample scope of the work and 

 its attractive typography and make-up, con- 

 stitute it a welcome addition to the text-books 

 of this division of physics. 



D. W. Heeing 



The Nature and Development of Plants, by 

 Carlton C. Curtis, instructor in botany in 

 Columbia University. Henry Holt & Com- 

 pany, publishers. 



Though published last year, the book has 

 not yet received, in the way of review, the 

 notice which it deserves. Though not pur- 

 porting to be a text-book, it nevertheless is a 

 book which may well serve the purpose in the 



