ON SEISMOLOGICAL INVESTIGATION. 



161 



The following table of distances from Hekla, in Iceland, to places 

 whei'e movements were observed, together with the times at which the 

 latter commenced, shows that it is impossible to make any reliable calcu- 

 lations respecting the velocity with which motion was propagated. The 

 causes of the discrepancies are probably to be found in the diflerences in 

 the form of the instruments employed, and the want of a sufficiently open 

 time scale on many of the record- receiving surfaces : — 



KnoR. 

 Shide 1,831 



Strassburg 

 Padua 

 Rome . 

 Lschia 

 Catania 



2,368 

 2,775 

 .S,182 

 3.367 

 3,747 



ir. 

 11 

 11 

 11 

 11 

 11 

 11 



M. 



23 

 22 

 30 

 23 

 30 

 25 



s. 



48 

 9 

 

 



54 

 4 



Earthquake Iso. 36 (N.E. Japan, Nambu'). 



For the phases of this earthquake as recorded at Carisbrooke Castle 

 and at Shide, see 'Report of the British Association,' 1896, pp. 229, 230. 

 The photogram is repi-oduced in this Report, p. 142. 



This shock created considerable destruction in the north-west part of 

 Nippon. It was recorded in Tokio as a slow horizontal movement with a 

 slightly vertical component, but the records from ordinary seismographs 

 v/ere too small for accurate measurement. The time of its commencement 

 in Tokio was, in local time, 5h. 9m. 33s. P.M., or in G.M.T., 20h. 9m. 33s. 



When this motion was recorded the disturbance would have advanced 

 4° on its path towards Europe. 



The time taken for three of the various phases of motion to reach 

 Shide and the Isle of Wight, and the velocities of propagation, were as 

 follows : — 



and 



Because earthquake movement dies away gradually and fitfully, it is 

 not at all remarkable that there should be nearly 27 minutes difference in 

 the recorded duration of the disturbance as shown at Carisbrooke and 

 Strassburg. The differences between the two records which are noticeable 

 are in the times at which the preliminary tremors commenced and their 

 duration. Because Carisbrooke is not more than 360 kms. fai'ther from 

 North Japan than Strassburg, it might be expected that the preliminary 

 tremors at the latter place would have been observed about half a minute 

 before they reached the Isle of Wight. A difference e.xceeding five 

 minutes either indicates that the Carisbrooke instrument is less sensitive 



1597. 



Nature, April 15, 1897, p. 558. 



M 



