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XXXVIII. Notices respecting JSew Books. 



Studies in Terrestrial Magnetism. By 0. Chree, M.A., Sc.D. 

 LL.D., Sup3rintenient of Kew Observatory - , etc., etc. Mac- 

 millan's Science Monographs. Macmillan & Co., Ltd. : London, 

 1912. Pp. xii + 206. 



npHIS volume is " intended to give a connected account " of the 

 -*- author's "own original work" in terrestrial magnetism, 

 without aiming at being a text-book or even at summarizing the 

 results of other investigators in those branches of: terrestrial 

 magnetism with which it actually deals. The author gives us 

 " almost entirely facts, or supposed facts." Absence of theory is 

 by no means due to lack of curiosity as to " the causes of things," 

 but to the author's well-founded belief that for the time being 

 theorising is less promising than the extension of "positive 

 knowledge." 



The book being mainly concerned with results derived from 

 magnstogramSf the author gives in Chapter I. a useful explanation 

 how such records are obtained and interpreted. The next chapter 

 is dedicated to Secular Changes of the magnetic elements ; the 

 subject is illustrated by tables and a diagram extending from 1860 

 up to 1910. Chapter III. deals with Non-Cyclic Changes, and 

 Chapter IV. with Diurnal Inequalities, obtained by taking in 

 succession the difference of each hourly value from the mean 

 of the twenty-four; here, as in the remaining chapters, many 

 numerical data and several diagrams are given. Chapters V. 

 and VI. are dedicated to Diurnal Inequality on Ordinary, and on 

 Disturbed Days, respectively. The next chapter treats of the use 

 of Fourier series for the representation of diurnal inequalities. 

 Although this method is to be employed with discernment, the 

 author agrees with the well-established opinion of investigators of 

 other branches of terrestrial physics that " even if there should 

 be no natural force answering to each term of a Fourier expansion, 

 a study of individual terms of the series may prove of marked 

 utility." Chapter VIII. deals with Annual Variation, and 

 Chapter IX. with the Absolute Daily Range, i. e. the excess of 

 the largest over the smallest value during the twenty-four hours. 

 Comparatively much space is dedicated to Antarctic Magnetic 

 Eesults (Chap. X.). Chapters XL and XIL, dealing with Mag- 

 netic Storms and their " sudden commencements," contain a 

 number of very interesting curves which are likely to attract 

 the attention even of non-specialists. Of equal interest will be 

 the Comparison of Arctic and Antarctic Disturbances, treated in 

 Chapter XIII. , in which the author gives us numerous Kew-curves 

 juxtaposed with Birkeland's arctic, and corresponding antarctic 



Phil. Mag. S. 6. Vol 32. No. 189. Sept. 1910. 2 A 



