38 



The Icvor was pivotti-d to a fixed -iip|)iirl l>y a Kail and .<ock(t joint, and con- 

 nected to tlic [HMiduluiii l)y a iiall and tnlu' joint. The motions of its lon<r end 

 were rej^isterod by its pidlinj;- up a thread throujjh a hole in a plate lixed 

 immediately holow it. The threa<i was wound round a lit;ht pnllev to whieli an 

 indieatinjf pointer was attaeheil. Another jiendnlum instrument was arranged 

 with eiiiht indices, and was desiirned to give the direction of the jiorizontal 

 dis])lacenient. Dr. AVagener's .s<jhen>i' also included a eontinuouslv registering 

 seismograpli, in wliich the motii>ns of a peu<luhun were to he recorded on a 

 drum, started into rotation i)y tlie earth(|uake, and travelling longitudinally as 

 it revolved, hv means of a screw on its axis. This jiart of the jilan does not 

 appear to he been put in practice.* 



§ 37. Long Pciiiliiliiin Sfisinograpli . 



A long jH'nduUim seismograpli provided with a pair of multiplying lever.s 

 Uv which two comixinents of the horizontal motion were recorded on plates kept 

 in continuous motion hy a clock, was designed and erected hy the ))re,seut writer 

 in 1K7II. Of this instrument, which was pidhaiily the earliest eontinuouslv 

 recording .seismograph to be actually con.structed and succe.s,sfnlly used, a de.scrip- 

 tion will be found in Vol. I of the Tran.sactious of the Seismological .Society of 

 Japan. Separate smoked-glass plates were used to receive the traces of the two 

 pointers. This introduced certain practical difficulties, and the original arrange- 

 ment was also objecticmable on account of the smallues.s of the plates. A 

 modified form has since been ado}>ted, and is now in use in the writer's observa- 

 torv. The in.strument as it now stands i.s shown in Plate VIII. 



Fig. 24 give.s a general view of the structure by which the point of suspen- 

 Siion of the ])endnlnm is sup])orled. It consists of a very rigid wooden frame- 

 work, firmly founded on piles, and rising above the ground to a lieight of over 

 six metre.«. This is completely detached from tiie walls and roof of the building- 

 in wiiich it stands. The pc ndnluni con.-ists of a massix-e ling of cast-inm n, 

 weighing 'iö kilogrammes, and hung in a horizontal plane from the top of 

 the framework, bv three wins bl>l>. \ screw and nut at the top allow the 

 height of the rinsj above the ground to l)c adjusted. To record the motion of 

 the earth relatively to the "steady point' of the pendulum (which is, of course, 

 its centre of percu.ssion I two appliances are provi(k!<l, which may be u.sed either 

 alternatively or both togetln'r. In one of these the complete horizontal motion 

 is recorded by a single pointer: in the oth(>r, two rectangular com]>onents of the 

 horizontal motion are recorded by .separate pointers, but on the same plate. The 

 first arrangement only is shown in fig. 24, and is al«) shown, on a larger .scale, 

 in figs. 2Ö and 2f). The second arrangement is shown in figs. 27 and 28. 



The ring-bob of the pendulum (shown in section in fig.s. 2Ö and 27, and in 

 plan in figs. 26 and 28) carries an iron bar c across one of its diameters, in the 



* Trans, of the Sei.smoloairal Society of Japan, \'ol. I. p. 54 and \'ol. Ill, p. 107; also 

 Mitthoihingpn Acr deutschen Gesc(l.<cli!ift fiir Natnr- und Vüll<prkuiide Ostafien'.s, 1878 and 1879. 



