ME. MALLET ON THE TEANSIT- VELOCITY OE EAETHQHAEL WAVES. 675 
11 76 '40 7 feet per second for the transit>rate. The results, however, obviously form 
two groups, \iz. Nos. 1, 2, 3, and 6 from the smaller charges of powder, and Nos. 4 and 
5 from the greater ones. 
The mean from the four first is 1088 ’5597 feet per second, and that from the two 
last is 1352T015 feet per second; and taking a mean of means from both of these, we 
obtain a final result of 1220 '3306 feet per second as the mean transit-velocity of propa- 
gation, in the rocks expei-imented on, of a wave-pulse produced by the impulse of a 
charge not exceeding 12,000 lbs. of powder. We may be justified in concluding that 
the velocity of wave-propagation (or transit) really does increase with the force of the 
original impulse; it would be vain, however, to attempt to deduce the law of such 
increase from the results before us. 
The experiments of Mr. GoLDiXGHAii at Madras, on the retardation of sound in moist 
air, and the theoretical researches of Mr. Eaknshaw, both, by analogy, rendered a 'priori 
probable the fact itself, now for the first time, so far as I am aware, experimentally 
shown. 
It follows, then, on reference to my former experiments at Killiney Bay, that the rate 
of wave-propagation in highly stratified, contorted and foliated rock is intermediate 
between that for dense wet sand and for discontinuous and shattered granite. Adopt- 
ing the first mean from the smaller charges of powder, as better comparable with the 
Killiney experiments, which were made with charges of only 25 lbs. of powder, and 
which would doubtless have given higher velocities with heavier charges, we obtain the 
following series : — 
Transit-rates of Wave-propagation. 
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 I664'574 feet per second. 
We may infer, even adopting the highest mean of these experiments, 1352-101 feet 
per second, for comparison with the transit-rate for discontinuous granite, and bearing 
in mind that the former velocity is due to the impulse originated by a 'mean charge of 
9100 lbs. of powder, while the latter was due to one of but 25 lbs., that for equal origi- 
nating impulses the rate of propagation of waves analogous to earthquake waves of 
shock must be less, generally if not always, in contorted stratified rocks than in crystal- 
line igneous rocks analogous to granite, the amount of shattered discontinuity being the 
same in both. 
The general mean obtained, viz. 1220-33 feet per second =13-877 statute English 
miles per minute, coordiaates, as might be expected, with the more trustworthy of the 
older attempts to determme the velocity of propagation of earthquake-waves in nature^, 
and still more so with the more recent and exact determinations of such velocities made 
* See Table 8, “ Second Eeport on Earthquakes,” &c., Eeport of Brit. A ssoc. 1851, p. 316. 
