Page:McClure's Magazine volume 10.djvu/419

Rh since the other stations working with us have similar information. So many miles from Shide, and so many miles from Batavia, and so many miles from Argentina, and we must, with the help of a pair of compasses on the map, fix the place beyond question. And that is why it is desirable to have as many observatories as possible in different parts of the earth. Who can say, for instance, what great sums might be saved cable companies if they knew the precise boundaries of danger regions in the ocean's bed?"

"Are such regions well marked?"

"So well marked that a blind man could pick them out by running his fingers over a map of the ocean's bottom made in relief. Wherever he found sudden slopes going down from hundreds to thousands of fathoms, he could say with confidence, 'There is one.' We know in a general way some of these dangerous regions—there is one off the west coast of South America from Ecuador down; there is one in the mid-Atlantic, about the equator, between twenty degrees and forty degrees west longitude; there is one at the Grecian end of the Mediterranean; one in the Bay of Bengal; and one bordering the Alps; there is the famous 'Tuscarora Deep,' from the Phillippine Islands down to Java; and there is the North Atlantic region, about 300 miles east of Newfoundland. In the 'Tuscarora Deep' the slope increases 1,000 fathoms in twenty-five miles, until it reaches a depth of 4,000 fathoms.

"There have been submarine earthquakes here, like that of June 15, 1896, that have shaken the earth from pole to pole; and more than once different cables from Java have been broken simultaneously, as in 1890, when the three cables to Australia snapped

in a moment. And the great majority of breaks in the North Atlantic cables have occurred at the place just indicated, where there are two slopes, one from 708 to 2,400 fathoms in a distance of sixty miles, and the other from 275 to 1,946 fathoms within thirty miles. On October 4, 1884, three cables, lying about ten miles apart, broke simultaneously at the spot. The significance of such breaks is greater when you bear in mind that cables frequently lie uninjured for many years on the great level plains of the ocean bed, where seismic disturbances are infrequent."

Then the Professor went on to explain in detail how the cables are broken by these submarine earthquakes, the two chief causes being landslides, where enormous masses of earth plunge from a higher to a lower level, and in so doing crush down upon the cable, and "faults," that is, subsidences of great areas, which occur on land as well as at the bottom of the sea, and which in the latter case may drag down imbedded cables with them. Statistics show that fifteen breaks in Atlantic cables between 1884 and 1894 cost the companies about $3,000,000, and it is estimated that if the whole coast line of the world was looped with cables, as may be the case some day, there would be not less than three hundred interruptions annually from seismic disturbances.

It is evident, then, that as the laying of ocean cables increases, it is of the first importance that cable companies be in possession of the best available knowledge as to the more dangerous regions in the ocean's bed and the safer regions. This knowledge can come only through the study of such phenomena as are being investigated now at the earthquake observatories of the world.