51 



ill till' iiMiiki.il iimlli|)lviiii:; Icvir /. This livir i> iiiiiLirii alioiit m UmiI linri/un- 

 t:ll axis at III, its l»'ariii;^s liciiiii- carrird liy a lirarkit n stauiliii^ (Mil iVmn nnc 

 siili- of till' post. Till' l(iii}j;('r part of tlic li'vor is nf straw; and its InwiT riid 

 «•urric's a liiiigwl niarkinji- ]i(>iiiti.'r wlmse luuticnis arc rLrorik'd on tliu tiiiioUwl- 

 t;lass plate o. Tlie niiiltiplviiii;' ratio is 7 to I. 



Ill tliLs iustniineiit it is scarccly pi-artiralilc tn krcp tlir L;la-s platr i-i'volviii^ 

 «•oiitiiinoiisly. CiiantjC's of ti'iiipi ratiiir and uliicr causes iii;d<(-' tlu' ]iiill of llu' 

 spriiij^ K> variable that tlie oiiiililiriiiiu position is laicly constant for any Ioiil;- 

 tinu-, apart from ujvrtliqiiakc dis-tiirbaiicr. V^r Üv >:\u\v ria-dii static records air 

 iisi-li'ss; and the plan i.s adopted of startiiiij the plate into rotation as early as 

 |Kissil)l<' in the disturbance, liv inakinij the earthi|nake close an eleetiic eiiciiit 

 which releases a cat<'li and allows a iIiiviiiL;' clock to come into action. The 

 arranjienient will be desfribcd in a later chapter. 



Tlu' bob 1) inijrht of eoiirse lie jiivotted at the iiislantaiieoiis axis of the plate, 

 instead of beinjr fixed to the plate: but, as its diameter is small compared with 

 its distance from the axis of sii))port, we should liaiii little, in the way of steaili- 

 iies-, iiv this coinpiieation. The ma-s of the mulliplyiie^- lev<r is very small; 

 lit iierwise we .should place above its liin;j;e )it a coiintei|ioise which would raise 

 its centre of j^ravitv to the horizontal plane coiitaiiiiiiLT the liiii;;e, in order to 

 jtrevent a horizontal displaeeineiit of the j;iound IVoni prodiicini;- any niolion of 

 the system. 



S 4H. Hijdrmncti.r \'i:i-llrnl-Miili(iii Si l-:iiiiii/i-iipli. 



A pri>po>eil in^triinient i~ de-eribed bv Mr. (ira\' iindi r llii> liile, in llie 

 I'hilosopliical Majfazine for .Sept. INSI. ,\ii eiilai':;'ed liydroniei.r, wiili.i narrow 

 projectinji end, is immersi.'d in a lii|iiid, and weighted to have a slow period of 

 vertical vibration. If is coii<tr;iined to move in a vertical line only, and the 

 projiH-tinjjj end is connected to a marking;- index.* 



The sum; ob.s<'rver has also attein]ited to reJri^ter the vertical motion diiriii;: 

 earlliipiakes by iisiiifj a metallic vessel with a corrugated bottom, tilled with 

 lii|iiid which call iwillate vertically on account of the flexibility of the bottom of 



the Ves.-<d. 



J5otli of these arniiv^'cmenls are imi|iie.-lioiiably much le.-s practicable than 

 the loiided liori/.oiiial bar, rendered nearly a-talic either by Mr. (iray"s or the 

 present writerV nietlio<l, and they may therefore lie passed over with the briele.st 

 mention. 



" A liiiuy, frun lu »ink iiml riiii- in ii liili of wulir, hml Ici'h provioiiNly iiri>(I an a vvrtiuul- 

 iiiutiuii auisiiiuiiivlür l>)' Pr, Ii. \Vu)ri.-ia'r. (Tmiix, Si'Ik. .Sue. ur,lii|iuii, \'i>l. I, \i. lil.) 



