extraordinary Agitations of the Sea* 49 



accounts for the first efflux and the first influx of these extraor- 

 dinary oscillations, the succeeding effluxes and influxes being 

 merely as the continued oscillation of a pendulum when once set 

 in motion. Thus we see why these agitations generally com- 

 mence with an efflux on our coasts and in our lakes ; and why 

 the waters rise into heaps in the centres of lakes, and then flow 

 back to their shores. 



Sometimes during these oscillations of the sea subsequent 

 submarine shocks interfere with the effects of preceding ones, 

 and retreating currents meeting advancing ones may occasion 

 those " mountainous breakers " (as Darwin calls them), or those 

 " great sea-waves " (as Mallet calls them), which occurred at 

 Newlyn and Lamorna in 1755, as already stated. Nor is it 

 unusual for a shock on dry land to be succeeded by another after 

 a short interval; indeed each of the shocks in Cornwall on the 

 21st of October, 1859, and the 13th of January, 1860, was fol- 

 lowed by a second shock about an hour afterwards — the former 

 at Truro, the latter near Liskeard. 



I am unable to understand how any " long flat swell," moving 

 onwards according to the laws of ordinary waves, and arising, 

 as Mr. Mallet supposes, in the deep sea, or from a " submarine 

 volcano " hundreds, nay, thousands of miles off, but which has 

 never been observed, could ever have produced such agitations 

 on our coasts or in our harbours. How, for example, could it 

 have produced such and so frequent disturbances at the piers 

 of Penzance and St. Michael's Mount, only two miles apart, and 

 yet none has been observed on the broad and almost horizontal 

 shore midway between them? Or how could this "long flat 

 wave" or those successive "ring-shaped waves" propagated from 

 a centre, the " seismic vertical " in the deep ocean near Japan, 

 and moving towards all the points of the compass, produce such 

 effects in a Japanese harbour and likewise in some American 

 harbours nearly 5000 miles off, without occasioning similar 

 effects also in most of the harbours within 2000 miles of Japan? 

 Besides, if this " long flat wave " had any existence, it would 

 invariably, the very moment it reached the shore, begin to flow 

 up the beach without any previous efflux; whereas these agita- 

 tions begin generally with an efflux lasting from five to ten 

 minutes, as did that at Plymouth, of 31st May, 1811, already 

 described, that at Penzance, of 5th July, 1843*, and that at 

 St. Mary's pier, Scilly, of 4th October, 18591% 



Judging from what has been actually observed, there seems 



* See ray letter describing this in the * Literary Gazette ' of 15th July, 

 1843, p. 464. 



t See the Tide-gauger's report in my work f On the Land's-end Dis- 

 trict/ p. 88. 



Phil Mag. S. 4. Vol. 31. No. 206. Jan. 1866. E 



