ON THE PACTS OP EARTHaUAKE PHENOMENA. 315 



From the extremely conflicting or imperfect accounts given, as to the di- 

 rections in which the shocks were observed, and hence the uncertainty as to 

 what places may be taken as extremes of each range, I am only able from 

 the above list to select four cases in which we can arrive at any conclusion 

 worthy of reliance as to the approximate rate of transit of this shock. 

 These are — 



Rungpur to Arrah, 290 statute miles, in 1 1 minutes = 26-363 miles per 

 minute. 



Monghyr to Gorackpur, 200 statute miles in 5 minutes = 40 miles per 

 minute : this was in granite a part of the way. 



Rungpur to Monghyr, 180 miles in 16 minutes = 11-25 statute miles per 

 minute. 



Rungpur to Calcutta, 220 miles in 16 minutes = 13-75 statute miles per 

 minute : this was chiefly in low alluvial deposits. 



The last instance I shall at present advert to is that of two ships at sea, 

 both of which experienced a shock within half-an-hour ; it has been pointed 

 out to me by my respected friend Dr. Robinson as noticed in the Nautical 

 Magazine for March 1851, p. 165. Lieut. Maurj^ of the National Obser- 

 vatory at Washington, in noticing the existence of a submarine volcano, .as 

 observed by Captain Ballard of the ship Rambler, from Calcutta, on the 30th 

 of October, in lat. 16° 30' N., long. 54° 30' W., and Captain Potter of the 

 barque Millwood, last from Rio, half-an-hour later on the same day, when 

 in lat. 23° 30' N. and long. 58° 0' W., remarks, " These vessels M-ere about 

 520 miles apart ; supposing them in the direct line in which the earthquake 

 was travelling, its rate will appear to be about 1 mile in 5 seconds, which is 

 only a little slower than sound (at the rate of 1 mile in 4-6 seconds) travels 

 through air." 



It is possible there may have been two shocks, and that each ship's com- 

 pany felt a separate one ; but this is very improbable ; for as the ships were 

 only 520 miles apart, had there been, each vessel could scarcely have escaped 

 being sensible of two shocks ; assuming then it to have been a single earth- 

 quake, the rate is 520 miles in 30 minutes, or only 17-3 miles per minute. 

 In this case it is probable that the shock traversed (^quam prox.) horizontally 

 beds of loose material of vast depth at the bottom of the sea, and that the shock 

 thence was conveyed transversely upwards through the water to the ships. 



In the following Table I have placed together the results of all the pre- 

 ceding data as to the approximate rates of earthquake waves from obser- 

 vation. The value of this at present is simply that it affords strong pre- 

 sumptive confirmation of the correctness of the results of the preceding ex- 

 periments, and that both make it almost certain that the actual rate of transit 

 of earthquake-waves, when hereafter there shall be the means of their perfect 

 observation, as occurring in nature, will be found very much slower indeed 

 than I myself and others anticipated on theoretic grounds, based on the elastic 

 moduli of the rocky crust, considered as everywhere an unbroken elastic solid. 

 But as giving yet awhile correct ideas of the actual rates, the following 

 Table must be received as but most rudely approximate. 



With the exception of the Guadaloupe earthquake, upon which much 

 doubt rests, the greatest rate of transit in the foregoing Table falls greatly 

 below what would have been anticipated, on the assumption of the wave 

 passing through perfectly solid elastic bodies, while the general character of 

 the rates coordinate pretty well with the limits experimentally given in the 

 preceding pages. 



