284 ANNUAL OF SCIENTIFIC DISCOVERY. 



and thus indications afforded of the rate at which the shocks travelled. 

 In the Lisbon earthquake of 1761, the shock travelled to Corunna at 

 the rate of 1,994 feet, to Cork at the rate of 5,280 feet, and to Santa 

 Cruz, in Barbary, at 3,261 feet per second. The great Cutch earth- 

 quake, in 1819, stopped the clocks in Calcutta, and showed a rate of 

 1,173 feet per second. The Nepaul earthquake of 1834 stopped numer- 

 ous chronometers, and the rate of transit from the assumed centre to 

 various places showed a rate varying from 1,000 to 3,000 feet per 

 second. These rates were all lower than would be expected, consider- 

 ing rocks as homogeneous substances ; and, perhaps, after all, the 

 earthquake shocks might follow a law altogether different from that of 

 sound waves. Mr. Mallet then called the attention to the catalogue 

 of earthquakes, amounting to nearly 6,000, and exhibited diagrams 

 in which the amount of earthquake disturbance, in all known times, 

 was represented by curved lines ; these showed a slight indication of 

 paroxysmal periods, with intervals of a half century or more. A col- 

 ored map was exhibited showing the distribution of earthquakes, the 

 intensity of the color being proportioned to the frequency of these visi- 

 tations. On this map the regions of Guinea, Abyssinia and Madagas- 

 car were uncolored, no recorded earthquakes having occurred in them. 

 Greenland was uncolored, because the slight shocks felt there might 

 have been occasioned simply by the movement of masses of ice on the 

 coast. Especial attention was called to one spot in the Atlantic, near 

 the line, and midway between Guinea and Brazil ; vessels passing this 

 tract almost always experienced shocks ; the soundings were extremely 

 variable, some being obtained at 400 fathoms, whilst at very small 

 distances the depth was exceedingly great, as if the bottom was formed 

 by a group of volcanic mountains. The connection between earth- 

 quake lines and volcanic lines was very apparent on this map ; but 

 some earthquake regions, like Central Siberia, and a tract extending 

 from India to Bohemia, display very little volcanic energy. On a dia- 

 gram section of the globe, the most distant points at which great 

 earthquakes had been felt were connected by straight lines ; these 

 showed what very large portions of the map of the earth might have 

 been affected, supposing the original impulses to have been communi- 

 cated at any great depths. 



NEW VOLCANIC ISLAND IN THE MEDITERRANEAN. 



IT will be remembered that an island, about 120 feet high and 2.000 

 feet in circumference, suddenly sprang up in 1831 between Sicily and 

 La Pantellaria. It disappeared about a month after, and at a later 

 period even the sounding lead could give no indication of its existence ; 

 but vessels passing over the place it had formerly occupied would 

 sometimes feel a sort of shock, which showed that it was of volcanic 

 origin. In March last, however, the French vessel Eolc, which was 

 taking soundings in the vicinity, discovered some traces of its exist- 

 ence. Observations made since this time have verified the truth of 

 the preceding observation, and further discovered that the island, 



