706 Notices respecting New Books. 



right angles to the plane at the lower temperatures. A short 

 account of the dependence of this change upon the refractive 

 indices would have beeu welcome and instructive : instead of this, 

 the phenomenon is given merely as " a remarkable phenomenon." 

 Instead of describing the section of selenite used for the experi- 

 ment as "an oblique section," it would be more lucid to describe 

 it as one perpendicular to the first median line. Imperfections 

 of this sort may seem trivial, but in this chapter they occur fairly 

 frequently, and other chapters are not free from them. 



The first half of page 133, indicating a supposed dependence of 

 the order of possible interference upon the regularity of the 

 vibrations of the radiating molecules, merely states the antiquated 

 view, as though it were still thought to be correct. The correct 

 view, given by Rayleigh (also independently by G-ouy), appears 

 on p. 136 5 but the whole treatment requires to be modified so as 

 to remove the contradiction. 



New chapters have been added on Meteorological Optics, 

 Electro-optics, and the Principle of Relativity ; and considerable 

 changes have been made in some of the other chapters, chiefly in 

 the direction of additions to the experimental part, and a removal 

 of somewhat superfluous mathematics. 



With regard to the general appearance of the volume, the 

 reviewer cannot forbear from saying that it would be greatly 

 improved if more attention had been paid to some of the diagrams. 

 Many of these are simply rough script sketches, and they detract 

 very much from the general appearance. Some of these, again, 

 are on such a small scale as to be difficult to make out. 



The first edition was marred by a very large number of mis- 

 prints, chiefly of a fairly obvious kind in formula ; but, even so, 

 very confusing to a student. Many of these have now been 

 removed ; but, unfortunately, it must be stated that a number 

 still remain. Attention may be called to the numerical values 

 given for Eresnel's integrals on p. 247. These are quoted in an 

 erroneous form from textbook to textbook. The most important 

 errors are in the value of the cosine integral for v = 2'6 and 

 v = l-8: the former should be -3889 instead of '3389 (Tresnel's 

 value was -3895) ; the value for v = l*8 should be -3337 instead of 

 •3363 (Fresnel's value was "3312). Reference for other corrections 

 to these integrals may be made to D'Ocagne, Journal de Physique, 

 1902, p. 507, and to Wind, Physihalisclie Z&itschrift, No. 18, 

 p. 265. 



Orystalloqraphy and Practical Cn/stal Measurement. By A. E. 



H. Tutton, D.Sc, M.A., E.R.S., A.R.C.Sc. Pp. 946. 



Numerous illustrations. London: Macmillan & Co., Ltd., 



1911. Price 30/- net. 

 It is not very long since we received a small book dealing with 

 Dr. Tutton's own researches into crystal structure. The present 

 volume is of quite a different scope ; indeed, it provides a 

 complete account of the subject in all its aspects. It is a guide 



