?0 REPORT— 1902. 



and there are two cases where the differences are 2 and 3 minutes. 

 In the remaining four cases the diflferences are respectively 8, 97, 6, and 

 32 minutes. When the period of B was changed to 10 and then to 

 12 seconds, it seems to have been, out of eighteen cases, a matter of chance 

 as to which of the two pendulums first responded to the movement of the 

 ground. Twice they commenced simultaneously, and three times the 

 difference in the commencements was from 2 to 3 minutes. In all other 

 instances these differences are large. The times at which pronounced 

 phases of movement have taken place — for which tables are not given — 

 are practically identical for all the pendulums . 



In comparing amplitudes when the periods of A and B were equal 

 (17 sec), the amplitudes were either equal to each other or that for B 

 was larger by 0-25 mm. The only exceptions are for Earthquakes 608 

 and 609. 



When B was reduced to 10 and then to 12 seconds the amplitudes 

 ■were for all the larger disturbances, excepting 601, distinctly smaller 

 than those recorded by A. In other instances, relating to small earth- 

 quakes, these displacements were equal. 



A similar relationship between amplitude and period is seen when 

 comparing C and B. 



This result is one which does not accord with the result of a somewhat 

 similar experiment made by Dr. F. Omori, whilst it does accord with the 

 hypothesis that the large waves of earthquakes traverse the surface of 

 the earth in undulations. 



With equal periods for A and B, generally the latter was caused to 

 move for a longer time than the former, whilst when B was rendered 

 more stable this result was usually reversed. This again suggests that 

 the movements recorded are accompanied by tilting. 



VII. CUnometric Experiments. 



In 1891, whilst resident in Japan, I designed a clinometer to record 

 the tiltings of the ground which take place with severe earthquakes within 

 two or three hundred miles of their origin. The chief feature in this 

 instrument was a balance beam loaded at its extremities, which when its 

 frame was tilted in a direction at right angles to its length was assumed 

 to retain its horizontality. A pointer like that of an ordinary balance 

 attached to this beam acted as a steady fulcrum for the short arm of 

 a lever, the outer end of which rested on a smoked-glass surface. 



This is described, and illustrations of its records are to be found in the 

 ' British Association Report for 1893,' and in the ' Seismological Journal,' 

 ii. p. 103. 



In 1900 and 1901 at Shide, in the Isle of Wight, I set up a similar 

 but much larger clinometer, with the expectation that it would give some 

 definite information about the so-called large waves which are assumed to 

 accompany large earthquakes when they have radiated to great distances. 

 This 'experiment,' which is referred to in the 'British Association 

 Report' for 1900, p. 83, consisted in observing the movements of a 

 pointer attached to the earth relatively to a pointer, 4 feet in length, 

 attached at right angles to the beam of a balance, the arms of which were 

 5 feet in length, and each carried a load exceeding 30 lb. Any relative 

 movement of these pointers was shown by the displacement of a spot of 



