252 THEORETISCHE OPTIK. 



the student. An exception, however, must be made with respect to 

 the statements concerning the electromagnetic theory of light. We 

 are told (p. 450) that the English theory, founded by Maxwell and 

 represented by Glazebrook and Fitzgerald, makes the plane of polari- 

 zation coincide with the plane of vibration, while Lorentz, on the 

 basis of Helmholtz's equations comes to the conclusion that these 

 planes are at right angles. Since all these writers make the electrical 

 displacement perpendicular to the plane of polarization, we can only 

 attribute this statement to some confusion between the electrical 

 displacement and the magnetic force or " displacement " at right angles 

 to it. We are also told that Glazebrook's " surface-conditions " which 

 determine the intensity of reflected and refracted light are different 

 from those of Lorentz, a singular error in view of the fact that 

 Mr. Glazebrook (Proc. Camb. Phil. Soc., vol. iv, p. 166) expressly 

 states that his results are the same as those of Lorentz, Fitzgerald, 

 and J. J. Thomson. We have spent much fruitless labor in trying to 

 discover where and how the expressions were obtained which are 

 attributed to Glazebrook, but in which the notation has been altered. 

 They ought to come from Glazebrook's equations (24)-(27) (loc. tit.), 

 but these appear identical with Lorentz's equations (58)-(61) (Zeit- 

 schrift f. Math. u. Phys., vol. xxii, p. 27). They might be obtained by 

 interchanging the expressions for vibrations in the plane of incidence 

 and at right angles to it, with two changes of sign. 



The reader must be especially cautioned concerning the statements 

 and implications of what has not been done in the electromagnetic 

 theory. These are such as to suggest the question whether the author 

 has taken the trouble to read the titles of the papers which have 

 been published. We refer especially to what is said on pages 248, 

 249 concerning absorption, dispersion, and the magnetic rotation of 

 the plane of polarization. 



In the Experimental Part, with which the treatise closes, we have 

 a comparison of formulae with the results of experiments by the 

 author and others. The author has been particularly successful in 

 the formula for dispersion. In the case of quartz (p. 545), the 

 formula (with four constants) represents the results of experiment in 

 a manner entirely satisfactory through the entire range of wave- 

 length from 2*14 to 0*214. Those who may not agree with the 

 author's theoretical views will nevertheless be glad to see the results 

 of experiment brought together, and, so far as may be, represented by 

 formulae. 



