ON SEISMOLOGICAL INVESTIGATIONS. 69 
Seismological Investigations.—Seventeenth Ieport of the Com- 
mittee, consisting of Professor H. H. Turner (Chairman), 
Mr. J. Mine (Secretary), Mr. C. VERNON Boys, Sir GEORGE 
Darwin, Mr. Horace Darwin, Dr. R. T. GLAZEBROOK, Mr. 
M. H. Gray, Mr. R. K. Gray, Professor J. W. Jupp, Pro- 
fessor C. G. Knorr, Professor R. Mreupoua, Mr. R. D. Oxp- 
HAM, Professor J. Perry, Mr. W. E. PiumMer, Dr. R. A. 
Sampson, and Professor A. ScHusTER. (Drawn up by the 
Secretary.) 
[Puatrs I. anv II.] 
CONTENTS. PAGE 
I. General Notes—Registers—Visitors—New Stations—Situation of Zikawer 
PA GiaCOUNEIS Siig BCP oA l) ys Rede Meek WI 5 are 69 
Il. Seismic Activity, 1904 to 1910 inclusive, with map of origins : : Se TA, 
Ili. Relation of Amplitude in Seconds of Arc to the Distance of an Origin .  . 88 
IV. Direction of Earthquake Motion . Be eters: ae ey togee ox OU 
V. Relative Duration of Two Rectangular Components of Earth-Movement 
GING GUIEMUStAttOn) “YORI SEIMLE OEE. Re RBS EET Se icy Be 91 
VI. Megaseismic Activity and Periods of Quiescence . ‘ ¢ : F 4 
VIL. Megaseismic Frequency in Different Seasons . . ; Wits ae ie, ee? 
VIII. Earthquake Periodicity. . 94 
IX. On a New Periodicity in Earthquake "Frequency, by Professor H. H. Turner 95 
X. Intervals in Days from the Commencement of One Group to the Commence- 
ment ofanother . .  . 
XL. Intervals and Days between Successive Megaseisms in Particular Districts . 97 
XII. Geographical Distribution of Megaseisms and Thermometric Gradients. . 97 
XIII. A Possible Cause of Megaseismic Activity A AOE draw Ramee et nnle 40M 
XIV. Seismic and Volcanic Activity . . «© »© «© + «© + «= « 102 
XV. On the Mitigation of Air Tremors at Cardiff . : 3 : : : . 102 
I. General Notes. 
Tur above Committee seek to be reappointed with a grant of 601. 
During the last year the expenditure in connection with seismological 
work exceeded 320]. Out of this sum 200]. had kindly been placed 
at the disposal of your Secretary by the Government Grant Committee 
of the Royal Society. This covered the salaries of two assistants, with- 
out whom it would not have been possible to carry out the work at 
Shide and that connected with fifty co-operating stations. 
Registers.—During the last year Circulars Nos. 24 and 25 have 
been issued. They refer to Shide, Kew, Bidston, Guildford, Stony- 
hurst, West Bromwich, Haslemere, Edinburgh, Paisley, Eskdalemuir, 
Ponta Delgada, St. Vincent, San Fernando, Rio Tinto, Valetta, Cairo, 
Mauritius, Cape of Good Hope, St. Helena, Ascension, Fernando 
Noronha, Seychelles, Lima, Baltimore, Toronto, Victoria, B.C., 
Alipore, Bombay, Kodaikanal, Colombo, Cocos Island, Tokyo, Honolulu, 
Perth, Sydney, Wellington. 
Many of the Registers are received monthly. On arrival, the com- 
mencement and maximum of each disturbance they record are entered 
on a sheet opposite the date on which they were noted, and beneath the 
name of the station to which they refer. A glance at this table shows 
