920 



SCIENCE 



[N. S. Vol. XXXII. No. 834 



we can not help feeling that it is at most only 

 a question of time when MJme. Curie's admis- 

 sion will be effected; assuming, as no doubt it 

 may be assumed, that the opposition turns 

 only on the question of sex. It is hardly to 

 be supposed that this will be allowed, in our 

 time, to prevent for very long the recognition 

 of achievements of such unusual character, 

 and of such extraordinary importance in the 

 history of science, as those which she has 

 accomplished. Incidentally, it may be re- 

 marked that to the logical mind there will be 

 little to choose between her admission and her 

 non-admission, as an argument against the 

 views of those who still maintain that experi- 

 ence has shown women's incapacity for the 

 highest forms of scientific production. If she 

 is admitted, there will be one woman, out of 

 the handful that devote their lives to scientific 

 research, distinguished by one of the highest 

 of scientific honors; if she is kept out, it will 

 be one more proof of the immeasurable differ- 

 ence between the degree of encouragement and 

 incentive held out to women and that held out 

 to men for sustained devotion to strenuous 

 intellectual labors. — The N. Y. Evening Post. 



SCIENTIFIC BOOKS 

 An Introduction to the Theory of Optics. By 

 Aethur Schuster, F.E.S., Honorary Pro- 

 fessor of Physics at the University of Man- 

 chester. Second edition, revised. London, 

 Edward Arnold. 1910. 



The first English text-book on physical op- 

 tics which had any considerable utility for 

 college classes is probably that of Glazebrook, 

 published in the early eighties. Of the many 

 other texts and treatises on this subject which 

 have appeared since there is probably none 

 which shows better balance or more accurate 

 scholarship than the one of which the second 

 edition is now under review. 



We pass at once to some of the noteworthy 

 features of this treatment, and especially to 

 the changes introduced into the second edition, 

 merely pausing to commend the author's 

 clarity and precision of style. 



1. A nomenclature which has once been es- 

 tablished and which carries with it a perfectly 



definite meaning is dilficult to replace. But 

 every one must admit the cogency of Professor 

 Schuster's reasons for suggesting that we re- 

 place the term " simple harmonic motion " by 

 " simple " or " normal " oscillation, since 

 " harmony means a relation between different 

 things and not a property of any particular 

 thing." 



The term " quasi-homogeneous," which does 

 not appear in the former edition, is here intro- 

 duced to denote actual monochromatic radia- 

 tions met with in the laboratory as contrasted 

 with the hypothetical (homogeneous) radia- 

 tions described by the following equation, in 

 which X is unlimited as to value : 

 J/ = a cos 2Tr(t/T + !i)/\). 



As an illustration of the helpfulness of this 

 concept one may refer to the last paragraph 

 of art. 26, which is much clearer than the 

 corresponding paragraph in the older edition; 

 or' one may cite the following sentence from 

 the chapter on gratings : 



It is owing to the rapid falling off of light from 

 both sides of the principal maxima, that the 

 grating can be made use of to separate the dif- 

 ferent components of white light, and to produce 

 quasi-homogeneous vibrations. 



Another helpful term suggested (p. 60) in 

 the new, but not in the old, edition is the word 

 " coherent " to denote " vibrations which are 

 related in phase owing to their having orig- 

 inated at the same ultimate source." 



The following quantitative definition of 

 spectral purity appears in a new form; but it 

 is hardly self-contained or definite without 

 additional explanation. Spectral purity is de- 

 fined " as A/SA where 8A is the difference be- 

 tween two wave-lengths which just do not 

 encroach upon one another." 



2. In Chapter III. will be found a most in- 

 structive page of new material giving a com- 

 parison of the two methods of resolving white 

 light, namely, into pulses and into homo- 

 geneous waves. The essence of the matter is 

 contained in the following paragraph : 



The consideration of white light as a succession 

 of impulses is very instructive and often simpli- 

 fies calculations considerably, as we need only deal 

 with a single impulse; while if we start from the 



