55 



iif the cMllllijliril^i' >ll|)cr]Mi>iMl (111 the IiiiiM-]irriiMl wmvc.-- dllr (ii the swillLi' lit' llii' 

 ]iOll(lulilin. Tllr <;rc;itrst nctiliil (lis|il;ir('iiiciit ic;;i>tcri'(l liv tlir Xm lli-Smil li 

 iiKitidii poiiitiT was t\vi)-sL'voiitlis «iC a niilliiiutrt' : tlu' ntlwr pniiiti r .-linwcd no 

 iiiiiit' tlian a tiatr of motion. Tlusc irsiilts ngnx very closi'ly with tliosc «fivoii 

 liy till' otliir iiistrunKiit. 



If wc assume the jfivatcst (lisplaeeineiit to liavc takuii place a]>i>io.\imately 

 a<'<-<)r<ling to tlie simple liarmonic law, then, takinir tiie period as O.li second and 

 tlu; total i-an^e of motion as 0.:\ inni., we (ind for tlie lii'eatest velocity 1.Ö7 nun. 

 I'm;!- .-second, and for the jxreate.-t i"it<' of aeceleiati<in 1(!.4 mm. ])er second per 

 seconil. The value ol\(/ in the stme units is OTüT. Bodies eouueeted to the eaitli's 

 surface sullicieiitly rij^idly to move with it must therefore have experienced, in the 

 eartiniuake, a maxinunn hoi'izontal force eipial to about -jri'i „ of their own weiu;Iit. 



Alter de.srrihiiig (in the same |iaper) the records of fnin- other small earlh- 

 i|Uakes which als» occurred ihiring the mouth of November, ISSII, the writer 

 <Ire\v attention to the followin<r as the most .<trikinLC featiuvs of the.se early 

 observations: — "( 1 ) The very "fitidual Ijejrinning and endiufj of the disturliauce. 

 In none of the observations did the niaxiiiiiim motion occur until aftci' several 

 complete oseillatious had taken |ilaee. ( 2) Tlie irrcLiularity of the motion. The 

 succes-iive undulations are widely different both in extent and in pciiodif tiiiw. 

 ( ■■? ) The large uiuuber of undulations in a single cartlii|uake, and the cdiitiniKiiis 

 ehanicter of the sluK'k. (4) The extreme nunutene.<s of the motion nl' the 

 earth's .-inTaee." 



•; .')'.]. EitrlhiiwiLc iif FJiiiKiyij ilIi, y.V.S'/.* 



I'late XII i- llic iccKiiI iif a >mall carthijuakc, given liv llic leni/'.Miit.il 

 pi'iidulnm -ei>niograph (of the form described in § 2.'!). < >n tli is occasion ilie 

 displacement appeal's to have been coiilincd to one direction, (approximatclv F,a--t- 

 \\ e^t I : for this rea.HUi tlie tracings niaclc bv one ]ioiiiter onlv are reprcidnc« d 

 ill the I'iar«'. The gia.ss plate of the insdunieiii made one icvoliitidii in In I 

 H'coihIs, and the multiplying ratio was (i lo I. The visible di.-inrbance begins al 

 the jNiiiit f/, at the top of i'late X I I. The innermost of the two <arelcs visiiile on 

 the I'late is fliat wlii<-li tin' pointer was tiai-iug oiil prior to the eai tiii|Uake : on 

 it, at«, a feeble iiiidulatioii will be .h'cii to begin, and continue in the dirc<lioii 

 oftlic arrow, which is ilniwn op|)osite to the direction in which the plate was 

 revolving. It is not until aiioiit Iweiity-tive .si'coiids, or iiearlv a whole ipiadiant 

 of the glaw plate from the l)cginniiig of visible motion, thai the dispJMeenient- 

 Ih-coiuc at :dl ii>iisiilciab|e. TJi.. grcatist motion ociiirs at /Hat the bottom of 

 the I'latci. At that |M)iut the motion from one side to tlw other is (! mm. on the 

 ii;eord, eon<>| Minding to I mm. of actual horizontal motion of the gidimd, 



Tlie iindiilatioiis (nntinue with varying amplilnde for about I >J eoniphie 

 revolutions of the plalc. Thr late-t motion «liirh can be seen on lb«' record 



* S«c nl80 TniiH. of the Kcinmulogicnl Socioly orJii|>iiii, \i)(. Ill, i«. 11,5. 



