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Show HUNTING QUAKES j IS REAL SPORT Expert Observer Describes How Tremors Are Recorded. MECHANISM MUST BE PERFECT Seismograph Mutt Always De Kept Up to Concert Pitch, or After Weeks and Months of Waiting a Fine Record Rec-ord May Be Lost Distance Calcu. lated by Time That Elapses Between Be-tween Arrival of Primary and Secondary Sec-ondary Waves. Cntrhlng earthquakes by means of the seismograph Is n fnsiinatldg sport, writes .1. J. Shaw, of the West llrom-1 wlch SelMimlugtcnl Obion ntory In The London Dally Mall. One hum m-o that the cluck mechanism mech-anism nnd electric devices are always up to cniHvrt pltrli or lifter we ' nnd mou '.is of vuitiiig a Huh record may be lost. One Important observatory was caught unpplug recently. Earthquakes arc ruptures lu the earth's crust due to bending, crumpling and thrusts, stresses which nre common com-mon at the foot of mountain chains. The stresses accumulate, the strain becomes too great, Busily the rock strata fractures like on over-bent stick, and huge vibration Is set up sufficient suffi-cient to khakc down all structures In the vicinity; or, If sub-oceanic, to set up tidal waves and shake the crockery crock-ery on board ships as happens lu a house on land. Sets Waves In Motion. A shock sets up different types of wnves, which rush outward nt differ-1 ent speeds. There are three principal types , designated "P.," "S." nnd "L" "prl-l niary,"- "sccondnry" nnd "large,'' which attain to a "maximum" (M.), then Olo away. It Is from the time that elapses between the arrival of the primary waves nnd the secondary waves that the distance Is calculated. Thus: '" 100 "econds for 1,000 miles. KIM seconds sec-onds for 3,000 miles, 503 seconds fur 5,000 miles. The secondary wnves rarely survive after traveling 0,000 mile, when tho time betweVn "1'." nnd '.'I,." or "I'." and "M" though much less reliable, has to be resorted to. The only difllculty lies Ln iluterinlrf Ing from the record wh'eh oy.t of somo hundreds of. waives Is the pjrtl'eulnr ono required". The chief seismographs in-nsc nre: - Mi hie, British ; Milne-Shaw, British ; Galltzln, Busslan; Welchcrt, Herman;1 Miilukn, German ; Omorl, Japanese. Of these the Galltzln and the Mllne-rihaw Mllne-rihaw are the most sensitive. Tho first thrco record by a ray of light being photographed on sensitized paper; the last three by a gloss fiber writing on smoked paper. Clockwork keeps the recording sur-faco sur-faco always moving, nnd the time Is marked on elcctrlcnlly every minute. Locating the place of origin Is rather rath-er more dlflk-ult. Its direction, can he sometimes determined from one station sta-tion when the First Impulse Is well defined, de-fined, but much more reliable is the "thrco station" method. How They Are Located. Tho big shock of December 10 will serVc ns an example: Tho "S.-I. difference," ns the Indicating In-dicating time Is called, at West llrom-wlch llrom-wlch was 555 'Seconds, represcntlnj 4,8& miles. . .. Chicago, recently equipped with Milne-Shaw seismographs, sUted thcU distance to bo 3,000 miles.- . Circles drawn with radii of 4.88! nnd 3,000 miles from West Broinwlct and Chicago respectively intersect at two points, namely, Just south of, Alaska, 101 W. 64 N., and northwest: Brazil, 03 W. 4 N. A well placed third station with n third clrclo lsneccssary(-tjo determine whtcKr tho'two Intersections Is correct: cor-rect: 'No thlrtrfstation In n suitable position has so. far reported. 1ut the fact tjjrit Abcrdcch "received the first wavo 16 seconds earlier than West Bromwlch und Oxford 1 second Inter, fshV'wstjiat- tX;artUquokfl was In n r.no"rthe'cly dlrecilonjlellnU.ely deciding If nit' data tfo correct that' the eartnqtiake was m the bud of thd IA clflc ocenn, 300 miles south of Alnsk and 1,000 west of British Columbia. |