71 



For vertical movement, tlie pcndiiluin luib is liuiiij; hy a spiral spring just 

 above a continuous surface of mercury in a cup lielow, so tliat any vertical 

 vibration makes contact. Another form is a horizontal flat spring with a loaded 

 end, and a point on its under side which stands just clear of a mercury surface. 



A convenient form of the horizontal-motion apparatus is shown in sectional 

 elevation and plan in tigs. 38 and 30, Plato XXI. The pendulum n, consisting 

 of a fine wire and a lead bob with a jdatinum point below, is hung from the 

 top of the gla.s.s case b. The mercury is held in an iron cnp c (shown in section), 

 the height of which is adjustable by the serew J. One of tlic terniinais ea is 

 in elfctrical contact witli tlie pciuiulum, tiie cither with tiie cup of mercury. 

 The arrangement of connections preferred hy the present writer is shown in fig. 

 40. ^1 is the battery consisting of a single large "gravity" Daniell's cell. 

 It is kept always in circuit with the electromagnet B, whose resistance is 

 considerable. AViien the .seismoscope C acts the magnet is short-circuited, and 

 its armature is tlierei)y released. Tlie release of the armature can be used to 

 effect registration, start a record receiver, etc. 



This arrangement may appear less simple than to put the seismoscope int i a 

 single circuit with the magiu-t an<l iiattery, tlic circuit being tiien normally open, 

 but closed by an carth(|uake. The closed-circuit i)lan has, however, several 

 advantages; amongst which perhaps tlic nm.-t important is this, tliat any failure 

 of the battery is at once detected by the release of the armature. Any nund)er 

 of circuit-dosing .seismo.scopcs may, of course, be arranged its shunts to the same 

 electromagnet, -so that the armature will be released if any one of them acts 

 during an earthfjuakc. 



To render Palmieri's circuit-closer additicmally seiLsitive, Mr. Älilne has 

 added a multiplying arrangement, M'hich is shown in fig. 41, Plate XXI.* Any 

 deflection of the pendulum produces a magnified displacement of the h)wer end 

 of the lever /, which then makes contact with the mercury in the cup in. 



§ 69. Palmieri's Seitinic Apparatus, f 



An apparatus designed by Prof. Palmieri for the registration of small cutli- 

 fjuakrs was jilaccd by him in the oliscrvatory on Vesuvius in 18Ö6, and has been 

 I'or .some years in regular use in Jajian. It consists chiefly of several circuit-closing 

 «cisnioscopcs, with a dock to register the times of and intervals between distur- 

 bances, and a grou|> of U-tubes in dillercnt azimuths, which are provided with 

 indices to record tlii' dLsplacement of the mercury and also with circuil-clnsing 

 contacts. Tiie circuit-closers are arranged in two groiijis, fur horizontal and 

 vi'rtical motion respectively. The.se are connected Ui two electromagnets who.se 

 armatures carry a red and black pencil resjieetively, to mark the occurrence of 

 liorizontnl jmd vertical earthtpiake motions on a band of jiapcr pulled along 

 Ix'low them by clcx-kwork. This clockwork is start<'d by whichever of the 



* Tram, of the Sc'iHmological Sociotjr uf Jiipiui, Vol, IV, p. 08. 



t SimnogrophcA Klcctro-mBgn6ti(|uc« do Louis Palmieri, Naplcfl, 1878. 



