ON THE EAKTHQUAKE AXD VOLCANIC PHEXOMEXA OF JAPA.N. IGl 



expended in throwing up a jet of water 330 feet in height into the air. A 

 point well worthy of notice is the fact that the gunpowder waves had 

 a more gradual increase than those observed in shocks produced by 

 dynamite ; in other words, the former had a closer relationship to what is 

 so often observed in the records of actual earthquakes than the latter 

 had. 



3. JExperiments q/"MM. Fotjque and Levy. 



In the experiments of MM. Fouque and Levy the velocity of vibrations 

 on the surface and underground was determined by recording the intervals 

 between the shock which was usually produced by the explosion of from 

 4 to 8 kilos, of dynamite, and the displacement of an image produced by 

 a I'ay of light on a photographic plate moving with uniform motion. The 

 ray of light was reflected from a surface of mercury at the receiving 

 station. The highest velocity was obtained between a point underground 

 and the surface, along a line of 383 metres in length, which gave a velocity 

 of 2,.526 meti-es. In this case the shock was due to an explosion of 8 kilos, 

 of dynamite. 



The general results obtained were as follows : — 



The velocity evidently increased with an increase in the amount of 

 explosive employed, and it was greatest in the more elastic rocks. 



The discrepancy which exists between the above and Mallet's deter- 

 mination for granite (507 m.) only disappears if we compare it with the 

 second maximum in the photographic record (32.5 m. to 543 m.). 



The second set of experiments, considering the nature of the material 

 in which they were obtained and the smallness of the charges employed, 

 give remarkably high results, the velocity for the first maximum exceeding 

 that obtained by firing a larger charge of dynamite in granite on the 

 surface. In a single experiment to determine the velocity between a 

 lower and a higher level underground, the direction of the wave path is 

 unfortunately not very diflFerent from that of the stratification, and there- 

 fore is not comparable with those velocities along paths from the upper 

 level nearly transverse to the stratification between it and the surface. 

 If we are allowed to accept the results of Mallet's experiments, which 

 show that the velocities in these two directions are in round numbers as 

 1 "8 : 1 -0, then we may conclude that the velocity between the lower level 

 and an upper level was markedly greater than it was from the latter 

 upwards to the surface. 



These experiments show that the velocity between two points on the 

 surface is less than it is between the surface and a point underground. 

 They also indicate that the velocity with which vibrations are transmitted 

 may vary with the depth of the wave path. 



1895. M 



