355 



taking a mean of means from both, we obtain 1220*3306 feet per 

 second as the mean transit velocity of propagation, in the rocks expe- 

 rimented on, of wave pulses due to the impulse of explosions of 

 not exceeding 12,000 Ibs. of powder. 



The first mean from the smallest charges is that which must be 

 compared with the Killiney Bay experiments. It thus appears that 

 the wave velocity in highly contorted and foliated rock is very low, 

 and is intermediate between the transit rate in wet sand and in dis- 

 continuous granite, or 



In wet sand = 824-915 feet per second. 



In contorted and stratified rock, quartz, and slate = 1088'559 

 feet per second. 



In discontinuous granite = 1306*425 feet per second. 



In more solid granite = 1664-574 feet per second. 



The general mean obtained, 1220'33 feet per second, or 13*877 

 statute miles English per minute, co-ordinates, as might be expected, 

 with the carefully made deductions of Nb'ggerath and of Schmidt 

 from the actual earthquakes of the Rhine and of Hungary, as well 

 as with those of the author from the great Naples earthquake of 

 1857. 



In experimenting with these great explosions the author was en- 

 abled to observe, by means of the seismoscope, that the advent of 

 the great wave of impulse (which was sometimes sufficient to make 

 the mercury sway visibly in the trough of the instrument) was pre- 

 ceded by rapidly augmenting tremors, quite like those which very 

 generally precede the great shock in natural earthquakes. 



The wave transit in these experiments was made partly in slate 

 rocks and partly in quartz formations, which, though lithologically 

 and geologically distinct, are nearly identical in wave propagative 

 power (as this author has shown by a train of special experiments 

 at the conclusion of the paper), differing not more than in the ratio 

 of 0-576 for the slate to 0-558 for the quartz. The author concludes 

 by pointing out several deductions having interest to general physics, 

 and some of the special relations of the results to Seismology and 

 Physical Geology. 



