204 LIGHT SCIENCE FOR LEISURE HOURS. 



subterranean action ; but there can be no doubt it was 

 very deep indeed, because otherwise the shock felt in 

 towns separated from each other by hundreds of miles 

 could not have been so nearly contemporaneous. 

 Therefore the portion of the earth's crust upheaved 

 must have been enormous, for the length of the 

 region where the direct effects of the earthquake were 

 perceived is estimated by Professor Yon Hochstetter at 

 no less than 240 miles. The breadth of the region is 

 unknown, because the slope of the Andes on one 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 corn-field, 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 



