EARTHQUAKES. 179 



would, however, be desirable to ascertain once for all with 

 certainty what are the extreme limits between which the 

 velocities vary. It is probable that the more violent com- 

 motions by no means always possess the greatest velocity. 

 The measurements, moreover, do not always relate to the 

 same direction which the waves of commotion have followed. 

 Exact mathematical determinations are much wanted, and 

 it is only at a very recent period that a result has been ob- 

 tained with great exactitude and care from the Rhenish 

 earthquake of the 29th of July, 1846, by Julius Schmidt, 

 assistant at the Observatory of Bonn. In the earthquake 

 just mentioned the velocity of propagation was 14,956 

 geographical miles in a minute, that is 1466 feet in the 

 second. This velocity certainly exceeds that of the waves of 

 sound in the air ; but if the propagation of sound in water 

 is at the rate of 5016 feet, as stated by Colladon and Sturm, 

 and in cast iron tubes 11393 feet, according to Biot, the 

 result found for the earthquake appears very weak. For 

 the earthquake of Lisbon on the 1st of November, 1755, 

 Schmidt (working from less accurate data) found the velocity 

 between the coasts of Portugal and Holstein to be more 

 than five times as great as that observed on the Rhine, on 

 the 29th of July, 1846. Thus, for Lisbon and Gluckstadt (a 

 distance of 1348 English miles) the velocity obtained was 

 89.26 miles in a minute or 7953 feet in a second ; which, 

 however, is still 3438 feet less than in cast iron. 27 



27 Julius Schmidt, in Nb'ggerath, Ueber das Erdbebcn vom 29 Juli, 

 1846, s. 2837. With the velocity stated in the text, the earthquake 

 of Lisbon would have passed round the equatorial circumference of 

 the earth in about 45 hours. Michell (Phil. Transact, vol. i, pt. ii, 

 p. 572) found for the same earthquake of the 1st November, 1755, a 

 velocity of only 50 English miles in a minute, that is, instead of 7956, 

 only 4444 feet in a second. The inexactitude of the older obser- 

 vations and difference in the direction of propagation may conduce to 

 this result. Upon the connexion of Neptune with earthquakes, at 

 which I have glanced in the text (p. 181), a passage of Proclus in the 

 commentary to Plato's Cratylus, throws a remarkable light. " The 

 middle one of the three deities. Poseidon, is the cause of movement in 

 all things, even in the immovable. As the originator of movement he ia 

 called 'Eworriyaiog- to him, of those who shared the empire of Saturn, 

 fell the middle lot, the easily moved sea" (Creuzer, Symbolik und 

 Mythologie, Th. iii, 18.42, s. 260). As the Atlantis of Solon and the 

 Lyctonia, which, according to my idea, was nearly allied to it, are 

 geological myths, both the lands destroyed by earthquakes are re* 



K 2 



