48 REPORTS ON THE STATE OP SCIENCE. 



number of earthquakes since 1899 from these same districts, there- 

 lore, becomes A 40; B, 55; 0, 30; D, 28; E, 133; F, 175; G, 26; 

 H, 35; I, 5; J, 5; K, 141; L, 2; M, 86 (this includes small dis- 

 turbances); 0, 1; P, 0. 



The most pronounced megaseismic activity is at the present time 

 along a band running from the south extremity of the Philippines and 

 Java in an east-south-east direction towards the middle of the Pacific. 

 In the islands which stud this band with their intervening troughs 

 we see the outcrops of mountain ranges with Himalayan proportions. 

 It suggests a continent in the making. 



IV. A New Departure in Seismology. 



In the British Association Report, 1908, p. 64, I showed that 

 after the earthquake of January 14, 1907, which devastated Kingston, 

 Jamaica, 51 of the after-shocks were recorded by the British Association 

 type of instrument at several stations in Great Britain. The time taken 

 for these to travel from Jamaica to Great Britain, a distance of 67°, 

 was in all cases practically 43 minutes. I am not aware that any one 

 of these 51 shocks was recorded by other types of instruments either in 

 Britain or Europe. Previously to this, however, very large shocks had 

 been recorded as thickenings of traces near to the antipodes of their 

 origin, but this was the first time that small after-shocks had been noted 

 at places far removed from their epicentral areas. We have here not 

 only an indication of the high degree of sensibility possessed by a 

 certain type of instrument, but a suggestion that a new field for ex- 

 ploitation had been discovered. Observations corresponding to those 

 made on the shocks from Jamaica have been frequently repeated, with 

 the result that the registers from stations possessing different types of 

 instruments show considerable variation in the number of records which 

 they yield. For example, between July 1 and December 31, 1909, we 

 find that in the Isle of Wight 279 earthquakes were noted. These are 

 assumed to be of true seismic origin, either because each finds a cor- 

 responding record at several other stations, or that they were noted at 

 times when we should expect the surviving efforts of large earth- 

 quakes to arrive in Great Britain. During this period, at Hamburg. 

 Strassburg, and Laibach, where other types of instruments are in use, 

 the number of records were respectively 123, 64, and 42. At these 

 latter stations, like many others in the world, we find either instruments 

 recording on smoked paper or instruments which recorded photo- 

 graphically. In the former the writing pointers are connected with the 

 bob of a pendulum by a system of levers which gives a high multipli- 

 cation, whilst with the instruments which record photographically the 

 source of light is at a considerable distance from the record-receiving 

 surface. With the first type of instrument a slackness in joints, 

 together with elasticity and inertia of the levers, results in a loss of 

 motion. Where the multiplication is high the makers of these instru- 

 ments tell us that this amounts to five per cent. This means that no 

 record whatever can be obtained until a certain amplitude of motion 



