44 NINTH REPORT. 



prophecy was assured when, six years later, von Rebeiir-Paschwitz found 

 in the records of a horizontal pendulum certain abnormal movements which 

 he traced to earthquakes at great distances from the observing station. 

 The great Indian earthquake of 1897 was the first to be studied at distant 

 stations, namely, in Italy, Germany and Eiigland; ])ut today the globe is 

 (lotted with earthquake stations well distributed over its surface. Every 

 heavily shaken district whether accessible upon the land areas or upon the 

 bottom of the sea, has its shocks recorded not at one l)ut at many stations ; 

 and from these earthcjuake watch-towers it may be cpiite accuratel}^ located 

 through a very simple calculation. Thus, for example, an earthquake in 

 New Zealand telegraphs its own report to Professor Mijjie at his station in 

 the Isle of Wight, though this is almost exactly upon the opposite side of 

 the planet; and it occupies, moreover, but a little more than twenty minutes 

 in transmission. This first report is dispatched through the body of the 

 earth, but other and slower messages are sent along the surface with velocities 

 only one-third as great, and these arrive over the longer route some hours 

 after the first intelligence. Still later come the telegraphic reports of the 

 disaster, though these may be delayed for tlays as a conseciuence of ruptured 

 cables. 



The distant study of ''unfelt" (juakes has revealed to us facts of the first 

 order of importance. Of "world-shaking" carthcpiakes, comparal)le in in- 

 tensity to the one which visited California last April, we know that no less 

 than 70 occur each year, 90% of which are fortunately upon the floor of the 

 ocean. Each of these disturbances throws into agitation the entire earth's 

 crust, the surface movement being transmitted as a slow swell which even at 

 the most distant points has sufficient intensity to raise the surface of the 

 ground a number of inches, and would he perceived were it not so. slow. 

 The waves which first arrive at the earthquake station come by the direct 

 route through the earth's mass, and these have told us that the substance of 

 the earth's core is about H times as elastic as the best tool steel. To have 

 discovered a direct method of studying, upon the one hand, the interior of 

 our planet, and upon the other, geological changes which take place at the 

 bottom of the sea, will hardly be considered small contributions to the sum 

 of human knowledge. 



Fascinating as is this distant study of unfelt quakes, it is to the no less 

 interesting and more purely geological phases of our subject to which I wish 

 to draw" your attention this evening. The supposed dependence of earth- 

 (juakes upon volcanic sources of energy in its more concrete form has assumed 

 that gases are imprisoned at some place within the crust — a locus or center — 

 and in their struggles to free themselves they send out sharp seismic waves. 

 This focus or centrum idea has come down to us from the Greek philosophy, 

 and was common enough in the Middle Ages. When in Henry IV Glendower 

 boasts that the heavens were on fire and the earth was shaken at his birth, 

 Hotspur is made to say: 



"O, then the earth shook to see the heavens on fire, 

 And not in fear of your nativity. 

 Diseased nature oftentimes breaks forth. 

 In strange eruptions; oft the teeming earth 

 Is with a kind of colic, pinch'd and vex'd 

 By the imprisoning of unruly wind 

 Within her womb; which for enlargement striving 

 Shakes the old beldame earth and topples down 

 Steeples and moss-grown towers.'' 



