21 



in 1880* according ti> tlie |iiiiici|ilf,-; M't f'oitli in tlic nlxivc ]':ii:ii;i:i]ilis, and lias 

 liicn since (lien in alini'St enntiniKnis use at tlie I'niversity cf T kid. Its rvu- 



.-trucliidi will he nadiiv linderst 1 Iiv reference to I'late I, wliere litj. 1 gives 



an elevation and tig. "2 a plan of one of the horizontal ] endiihinis, and fig. 3 

 .shows in outline a plan of iioth and tlnir position with respect to the moving 

 gla.s.s plate. Each of the two |)reeisely similar horizontal ))eiidiiliinis consists of 

 a light iiiit rigid hrass frame «, a long jiointer of straw /), and a solid cylindrical 

 l)ras.s bob c. The fiamr n and ]iointer b are free to rotate togethi-r alioiit a 

 vertical axis dd (which is fixed to the earth and forms the axis of support), 

 being ])iv(ittc(l by a conical .steel juiint which works in a conical hole at tho 

 bottom, and by a conical hole at the top into which pres.ses a set-screw carried 

 by an inverted stirrup wliieii is in oin' jiiece with the liase-plate. In tig. 1, 

 one side of thi.s .-^tiniip i.s, for the .sike of clearness, sujipo.scd to be removed. 

 The bob c is pivottcd to the frame a in a similar manner, po as to be free to 

 rotate about the axis ee. The jioinfer /; is attached to the frame n at /, by a 

 joint which all(pws it to rise and fall verticallv, but not to move in a horizontal 

 plane excejit along with a. The frame a and pointer 6 together are proportioned 

 .-o tliat ee is the steady line (§ 17) relative to dd as axis of .support. Hence 

 when a .small horizontal displacement of the ground occurs transverse to the lever, 

 ee would (were it not for friction at liie juints and at the marking ])ointi'rl remain 

 stationary, even without th«; help of the bob r, and the inertia of the bob, pivottcd 

 as it is on the line ee, enormously increases the tendency of that line to keep 

 .«teady. For these movements therefore the line ee, and indeed the bob as a 

 whole, .serves as a standard of rest, and thev are recorded on a magnitied scale on 

 the smokcd-gl.Tss plate //, whicji is lightlv touched by a steel jmint at the end of 

 ihe straw /). Horizontal movements jiarallel to the length of this lever leave it 

 unatfecti-d, but an' recorded by the second lever, similar to the first, and set .it 

 right angles to it. Tiir two arc plai'cd so that their marking points tou<ii a 

 • ireiilar glass pl.iti- 7 ;it dilbrcnt distanees from its centre. By means of a clock 



• S««' I'roe. Itiivnl Socicly ofTxiiiiloii, No. "JlU, 1881, p. 440; iilso Trnii.s. of llicSeisni(iIi>j;Ical 

 Siicii-ly or.lapuii, Vol. II, p. 45. It appciirs tliiit llie parlicst iiUciiipt to apply tli« lioiizoiilul 

 p'liiliiluin lu llii! iiK-iisnri'iniMil ofcartlnpiiilo! inolioiiH wiis made- liy I'lof. W. .S. Clliapliii, of llir 

 l!nlv<Tnily ol'Tokio, alioiil 1S7H. H'ik appaniliis coiisi.sli'il ot'a wiioilcii roil, IVim) to linn alioiil a 

 viTlital avid, nii<l carrying at il.i c>iicl a rigidly allnc-liccl Mocli. It wa.s iiitcncli-il llmt llic iiiolion 

 of thc> Mirlh kIiociIcI lie ri-ciordicl liy a Iraciiij; point (ixcd to tlic Mcnk, wrcliiii; on a.>iinoolli siirfaci! 

 lixi'cl to llii- c-nrtli Udow it. Tlicrc wa.« no Mcnlliplicalion cd' llic: nicilion, and I'itlii-r for tili« 

 r<-aM>n, or Ix'iraii«!' friction «a« not Niillicii'iitly avoidi-il at tlic joints anci pointer, no results wen- 

 f'viT oliluiniHJ, Hii'l tin: apparatus was iiliaiidoiicd. 'I'lii- instriinicnt dcsirilccl in lli>- li'\t »a.s 

 ronKlnictt'il in till- siiiiiincT of 1880 and nrorded its lirst carilicjiiakir in Novcinticr of llic> saiiii! 

 yi-ar (we 'I'mii-acticiiis of tin; Asiatii- .Sc«iely of.lapaii, Vid. IX, p. 10). So far ilm tlie wHiit Ik 

 aware, no (ontiniioas reeord of eartlic|iiaki? niotioii liuci tieeii pn'vioiiHly olitiiiiied ley any olwerver. 

 Senile time l>efore its i*xliil>itioii to llie .Sidsinolo^ieal Socriety llie apparatus was sliown to Messrs. 

 .1. Milin- and T. 'tray, who ininiediatidy adoptecl it (willi iliu wiiler's ecniNeiil), unci liave sinic 

 *- III ployed it, willi slight idiaiiges in cic -tails of eons true lion, to in i -as lire artilicial as well as natural 

 • arlhipinlies, Ijiter. .Mr. (iray eoininiinieati cl a paper to the .SeisnioloKieal Soeiety " On .Sti-ady 

 I'oint.i for (■j>rthi|iiake Measiireineiits '' (Trans., \'ol. Ill, p. 1.), in «hieli lie deseriheil a iiiiiii- 

 livr of other coiitrivaiiceti i.-iiiliodyinK the same dynaiiiiual principleN (nee lielow, § § 27, 2'.) mid HI), 



