ON THE TRANSIT-VELOCITY OF EARTHQUAKE WAVES. 219 



The general mean derivable from the whole of the experiments taken to- 

 gether gives IITS'^O? feet per second for the transit-rate. The results, how- 

 ever, obviously form two groups, viz. 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 1352*1015 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 propagation, in the rocks experimented 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-pro- 

 pagation (or transit) really does increase with the force of the original im- 

 pulse ; it would be vain, however, to attempt to deduce the law of such 

 increase from the results before us. 



The experiments of Mr. Goldingham at Madras, on the retardation of 

 sound in moist air, and the theoretical researches of Mr. Earnshaw, both, by 

 analogy, rendered a priori probable what is 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. Adopting 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 

 been 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 Cquartzl ,„„„ -__ 



andslate) 1 1088*559 



In discontinuous granite 1306*425 „ „ 



In more solid granite 1664*574 „ „ 



We may infer, even adopting the highest mean of these experiments 

 (1 352*101 feet per second) for comparison with the transit-rate for discon- 

 tinuous granite, and bearing in mind that the former velocity is due to the im- 

 pulse originated by a mean charge of 9100 lbs. of powder, while the latter was 

 due to one of but 25 lbs., that for equal originating impulses the rate of propaga- 

 tion of waves analogous to earthquake-waves of shock must be less generally, 

 if not always, in contorted stratified rocks than in crystalline 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, coordinates, as might be expected, with the more 

 trustworthy of the older attempts to determine the velocity of propagation 

 of earth quake- waves in nature (see Table 8, " Second Report on Earth- 

 quakes," &c., Report of Brit. Assoc. 1851, p. 316), and still more so with the 

 more recent and exact determinations of such velocities made by Noggerath*, 

 who found it 1376 Paris feet per second; by Schmidtf, of the shock about 



* Das Erdbeben vom 29 Juli, 1846, im Rheingebiet, &c. V. Dr. Jakob Noseerath. 4to 

 Bonn, 1847. ^ ' 



t Untersuchungen uber das Erdbeben am 15 Jan. 1858. J. F. Schmidt, Astrouom, 

 Mittheilungen der Kais.-Konigl. Geog. Gesellschaft, II. Jahrgang, 1858. 



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