908 Dr. (J. Davison on the Annual and 



and for this region it may be shown from fig. 1 that roughly 



H cc v (y55 and E cc v 2 . 

 Consequently, 



HocR/^' 45 (9), 



There is, however, most probably a tendency for the relation 

 to take the simpler form given by Reynolds as the size of 

 the cylinders is still further increased. This follows since R 

 tends to be proportional to the square of the velocity, and 

 since Hughes found that the heat loss H tends to bo 

 proportional to v. 



January 1921. 



LXXXVI. r Ihe Annual and Diurnal Periodicity of Earth- 

 quakes in Japan. By Charles Davison, Sc.D* 



THE annual and diurnal periodicity of earthquakes has 

 been considered by several writers — by Prof. C. GL 

 Knott in 1886, by Prof. F. Omori in 1894 and 1902, and by 

 myself in 1893 and 1896 f. 



Since the year 1896, more complete records have become 

 available. The present paper deals with the earthquakes of 

 a limited area — the empire of Japan %. The method of 

 investigation adopted is the rough form of harmonic analysis 



* Communicated by the Author. 



t 0. G. Knott, "Earthquake frequency," Japan Seis. Soc. Trans. 

 vol. ix. pp. 1-20 (1886,; C. Davison, "The annual and semi-annual 

 seismic periods," Phil. Trans. 1893, A, pp. 1107-1169; C. Davison, 

 " On the diurnal periodicity of earthquakes," Phil. Mag. vol. xlii. pp. 

 463-476 (1890) ; F. Omori, " Annual and diurnal variations of seismic 

 frequency in Japan," Publ. Earthq. Inv. Com. No. 8, pp. 1-94 (1902). 



4 The' records analysed below are contained in the following cata- 

 logues : — 



Milne, J. (1), Japan Seis. Soc. Trans, vol. x. p. 61 (1887) ; vol. xiii. 

 pt. i. p. 93 (1889) ; vol. xv. p. 101 (1890) ; vol. xvi. pp. 56 and 83 

 (1892). 



Milne, J. (2). Japan Seis. Soc. Trans, vol. ii. pp. 4-14 and opposite 

 p. 38 (1880) ; vol. vi. pp. 32-35 (1883) ; vol. viii. pp. 100-108 (1885) ; 

 vol. x. pp. 97-99 (1887); vol. xv. pp. 127-134 (1890): Brit. Assoc. 

 Report. 1886, pp. 414-418; 1887, pp, 212-213 ; 1888, pp. 435-437; 

 1889, pp. 295-296 ; 1890, pp. 160-162 ; 1891, pp. 123-124 ; 1892, pp. 93- 

 95; 1893, pp. 214-215; 1895, pp. 114-115; 1897, pp. 133-137; 1898, 

 pp. 189-191 : 1899, pp. 189-191 : Brit. Assoc. Seis. Com. Circulars, vol. i. 

 pp. 29-30, 90-92, 142-144, 223-225. 



Milne, J. (S). "A Catalogue of 8331 Earthquakes recorded in Japan 

 between 1885 and 1892." Seis. Journ. Japan, vol. iv. pp. 1-367 (1895). 



