Measuring Earthquakes.

Taranaki Daily News, Volume XLVI, Issue 187, 12 August 1904, Page 2

Measuring Earthquakes.

INTERVIEW WITH PROFESSOR MILNE. Fr.r iroin the madding crowd, at Snide, near Newport!, Isle of Wight, in a region where dangerous seismic disturbances arc unknown, and amid beautiful scenery, Professor John Milne devotes himself to the study of earthquakes. In a quaint old country house, which, for his purpose, possesses the great advantage of resting on a solid bed of chalk that goes deep down into tlie bowels of the earth, he has erected instruments of his own devising winch make automatic records alike by day and by night, of every serious earthquake that takes place the suifacc of the earth. . • •' . No bookworm man of science is Professor Milne. He lias a big) head, but it rests on broad shoulders and a deep chest, and hisbionzed features till of long years of active outdoor life 'when he studied the earthquake In its chosen lair—Japan. Speaking to an interviewer recently Professor Milne said ; ~ "Of course an explosion of such tremendous character as that watch occurred at Martinique always makes the' earth shake in the vicinity, just as, on a smaller scale, does the discharge of a heavy gun. And it is extremely probatle that slight local carehuuakes accompanied it or followed it. "Hut their effects would have been mere fleabltcs compartH with the t#rrible havoc wrought toy, the tremendous outpouring of Aery lava and boiling mud from Mont I'elee, caused by the blowing otf of superheated steam from tho interior of the earth. "Asa m a tter of fact, earthquakes, so termed without any regard to their severity, are of very common occurrence': On an average, Bome.hing like 20,000 of them occur uu- .. jally. which is at the rate of over . o every twenty-five hours. •• Of these about 120 arc reallj earthquakes that amount to sonieUi.ng. And wherever Uiey take place, nt the North Pole or the /uitipodcs, or under the sea—where Vo per peat, of all earthquakes oc-cur-r-my instruments note them and make a record of them. "In the cool.ng-olf process that is continually going on in the inter ior of the earth there is a tendency to produce cavernous spaces in the cigittt above. Then when water filters into them from the earth, or gets in by capillary action from the sua. the superheated steam is produced, which, exercising tremendous pressure, linds a vent at the weakest spot, and the result is a violent vol.anic eruption. • As a bad patch on a boiler always invites disaster, so a pluggod-up volcano indicates the weak spot through which the subterranean forces, following the lino of least resistance, will again find a vent. •■' Earthquakes are of two kinds. Those which freuueiitly produce such calamitous results are due to the collapse or caving in of tho earth's outer crust over these hollow spaces;, just as a tunnel may full in. " The other, kind of earthquakes, which happily constitute the vast majority of them," lie continued, "are caused by fracturing due to the excessive bending of the earth's crust. These merely produce a slight elastic Shiver at the surface." After a twenty years' practical courselin earthquake study in Japan, Professor Milne returned to England and established his seismic observatory on the Isle of Wight. Roughly and briefly described, the instrument by which he obtains re* cords of them consists of a rigid Iron rodj the"*base of which is embedded in a solid foundation of masonry. From near the base of this rod extends anothor rod, weighted, and attached to it by a swivel somewhat similar to tho boom of a sailing yacht, line.most inlinitcsimal movement of the vertical rod sets the boom'rod swaying. At the'top' of this latter is a silver pointer, which mukes an impress on smoked paper passing over u cylinder revolving by clockwork, so that the exact timo at which a disturbance is recorded is also automatically noted. Professor Milne has several of these instruments at his seismic observatory of varying degrees of sensitiveness, some of them so delicately adjusted that thoy will record a deflection of one inch in ten miles. The mere pressure of the thumb on the •solidi masonry foundations will causo the tip of tho boom to move an inch Whenever an earthquake that to something occurs it despatches seismic waves right through 'this solid old earth of ours, and Professor Milne's instruments respond to the vibrations. Iho signals thus despatched by an eoithquake at the Antipodes will reach Professor Milne's observatory in twenty minutes. Simultaneously surfaco seismic waves are set in motion.

Such an adept is Professor Milne ■mi-eadmg these seismic hieroglyplmcs kle iTr°, bWn ,r * m tlu.-m some «loa of the duration and intensity of the earthquake ,vcorded. and approximately where it occurred Tlirough Ins efTorts upwards o. unity-six seismic observatories have the world, with which he is i„ Coln . munication.