224 LIGHT SCIENCE FOR LEISURE HOURS. 



side and the ocean on the other concealed the motion 

 of the earth's crust. 



The great ocean-wave swept, as we have said, in all 

 directions around the scene of the earth-throe. Over 

 a large part of its course its passage was unnoted, 

 because in the open sea the effects even of so vast an 

 undulation could not be perceived. A ship would 

 slowly rise as the crest of the great wave passed under 

 her, and then as slowly sink again. This may seem 

 strange, at first sight, when it is remembered that in 

 reality the great sea-wave we are considering swept at 

 the rate of three or four hundred sea-miles an hour 

 over the larger part of the Pacific. But when the 

 true character of ocean-waves is understood, when it is 

 remembered that there is no transference of the water 

 itself at this enormous rate, but simply a transmission 

 of motion (precisely as when in a high wind waves 

 sweep rapidly over a cornfield, while yet each corn- 

 stalk remains fixed in the ground), it will be seen 

 that the effects of the great sea-wave could only be 

 perceived near the shore. Even there, as we shall 

 presently see, there was much to convey the impres- 

 sion that the land itself was rising and falling rather 

 than that the deep was moved. But among the 

 hundreds of ships, which were sailing upon the Pacific 

 when its length and breadth were traversed by the 

 great sea-wave, there was not one in which any un- 

 usual motion was perceived. 



