ON SEISMOLOGICAL INVESTIGATIONS. 47 



Instruments in Jamaica {for local shocks). 



1. Chapelton (M. Maxwell Hall). — A duplex-pendulum seismometer. 

 Heavy weight, about 30 lb. Multiplication about 10 for horizontal 

 movements only. Records on top upon a smoked-glass plate. 



2. Kingston (Brennan). — Made after the pattern of Gray, of Glas- 

 gow. A heavy weight ring about 9 inches diameter, 25 lb. weight, 

 acts as a pendulum, with ' dampers ' to prevent continued oscillation 

 termed ' friction pointers.' Multiplication about 12. Eecords upon 

 a smoked-glass plate below, same as described in Milne's book on 

 earthquakes. All enclosed in a case free from wind currents. Length 

 of suspension about 5 feet. 



Verbeck's Ball and Vlate Seismometer. — Described in Milne's book. 

 Consists of two plates of glass 2 feet by 18 inches by £ inch, about 25 lb. 

 each, separated by three f-inch steel bars horizontally fixed. Eegisters 

 on the top surface of top plate. This will give the actual horizontal 

 movement of the ground, and is intended for large earthquakes. Can 

 register a movement of about 2 or 3 inches. Fixed firmly to the ground 

 and protected from air currents. 



III. Distribution of Earthquakes in 1909. 



The dash-dot lines on the accompanying chart (Plate I.) are parallel 

 to the axes of districts from which large earthquakes have originated. It 

 will be observed that they follow the principal ridges and troughs on the 

 earth's surface, but not necessarily to their extremities. 



In the Pacific the lines P, E 1( A lt A 2 , B, D L , and D 2 follow the 

 lines of troughs, while the remaining lines in the same ocean follow 

 ridges. In the Atlantic the eastern portion of C x and H are ridge lines, 

 whdst the western portion of C x is the portion of a trough. 



In Africa K 8 is a ridge, whilst O and its northerly continuation to 

 the Jordan depression is partly a trough. 



In the Indian Ocean part of G x and G 2 are parallel ridge lines, 

 whilst F 3 , F 2 , M 1( and E are troughs. 



The lines in Europe and Asia follow ridges ; K x is the Tian Shan- 

 Altai system, which is continued to the north-east by the Stanovoi- 

 Yabolonoi ranges. From this north-eastern extension, however, but 

 few earthquakes originate. K 2 is the Kwen Lun system, which ends 

 abruptly at the great plain of China or turns at right angles near the 

 great bend of the Hoango Ho and follows the fold of the Khingan 

 Mountains to the northern bend of the Amur. K 7 , K 4 , K 3 is the 

 Alpine, Balkan, Caucasian, Himalayan system, which turns sharply 

 round the eastern bend of the Brahmaputra, and as the Arakan Yoma 

 range runs down to Cape Negrais, to be continued by stepping stones, 

 the Andamans and Nicobars, to join the Sumatra-Java volcanic ridge. 



The number of earthquakes which have originated from each of 

 these districts in 1909 was A, 4; B, 3 ; C, 0; D, 6; E, 18; P, 24; 

 G, 3; H, 2; J, 0; K, 25; L, 0; M, 13; N, 0; O, 0; P, 0. The total 



