﻿Notices respecting New Books. 1G3 



are carried along by the clear and pleasant style and the manner 

 in which, step by step, the subject is unfolded. 



A detailed account of the book chapter by chapter would serve 

 no purpose, for it is certain that before long the book will be in 

 every laboratory and will be included in the curriculum of many- 

 teaching institutions. A few special points of excellency we will 

 notice. 



Some of the most interesting recent matter arises out of the 

 advances made by Professor Wood himself. While the place given 

 to this work is no more than it deserves, the collection of so much 

 of it together, for the first time, is a feature of no inconsiderable 

 value. 



The general plan of the work is to treat in the earlier pages the 

 more elementary aspect of the subject. In the later chapters a 

 fuller and more advanced study of the several leading topics is 

 offered. A good sample of the author's manner of handling his 

 subject will be got by reading, for instance, the elementary chapter 

 on Dispersion and then turning to the chapter on the Theory of 

 Dispersion. The latter is one of the most interesting in the book. 

 It would be difficult to make it better. The author's beautiful 

 experiments on the anomalous dispersion of sodium vapour are 

 used with telling effect in conveying an insight into the manner in 

 which experiment has been found to substantiate the dispersion 

 formula derived from electromagnetic considerations for a medium 

 with a single absorption-band, accepting the D lines as forming a 

 single absorption-band in the dense vapour of sodium studied in 

 the experiments. A careful examination of the Ketteler-Helmholtz 

 dispersion formula applied to the dispersive properties of quartz is 

 previously given. 



But it is invidious to pick out any one section of Professor 

 Wood's book for special commendation. The fresh and original 

 treatment which is the prevailing charm of the work is found 

 throughout. The chapter on Eefraction containing the experiments 

 on artificial mirage ; that on Interference of Light with its many 

 practical details and ingenious experiments ; on Diffraction ; 

 Rotatory Polarization ; and Magneto-Optics, wherein the Zeeman 

 effect is excellently dealt with ; the Scattering by Small Particles, 

 wherein much is new to textbooks ; the interesting treatment 

 of the topic of the Nature of White Light — a topic which 

 Lord Eayleigh has made of special interest to readers of the 

 Philosophical Magazine : all are excellent. Nothing can be more 

 beautiful than Professor Wood's shadow or refraction photograph 

 of a sound-wave reflected by a flight of steps as an illustration of 

 Lord Eayleigh's treatment of grating problems. All these chapters 

 are, singly, valuable expositions of the subjects dealt with. They 

 close with a review of results and theories of the Eelative Motion 

 of -Ether and Matter. 



There are in our opinion a very few sins of omission. We think 

 photo-electric effects and such experiments as those of Elster and 



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