Form of Seismograph, 361 



per minute, this being kept up continuously for the purpose of 

 allowing the magnitude and the time of occurrence of any dis- 

 turbance, which is of sufficient amplitude to leave a record, to be 

 accurately obtained. This obviates the unavoidable uncertainty 

 which exists as to the action of any automatic contrivance de- 

 signed to come into action at the time of the disturbance. The 

 time of occurrence is obtained by causing the siphon, D (figs. 1 

 and 3), to mark equal intervals of time on the paper ribbon. 

 The siphon is fixed to a light index-lever which is pivoted on 

 the end of the lever, E, and the link, F. The lever E turns 

 round an axis at G, and rests with its end in contact with the 

 wheel, H, which is fixed to the end of the hour-spindle of the 

 clock, K (fig. 1). As each tooth of the wheel H passes the 

 end of the lever E a mark is made on the paper, and the end 

 of the hour is distinguished by putting a larger or a double 

 tooth at that part of the wheel. The time at which an earth- 

 quake has occurred can thus be found by measuring the dis- 

 tance of the record of the disturbance from the last time-mark, 

 then counting the number of intervals from the last hour- 

 mark, and then the number of hours to a known point. It is 

 convenient to mark the hour once or twice a day on the paper, 

 so as to save trouble in the reckoning should an earthquake 

 occur. 



The ordinary rate of motion is much too slow for the record 

 to show the motions of the earth in detail ; and, as has been 

 already stated, this is obtained by automatically increasing 

 the speed at the commencement of the shock. The arrange- 

 ment for doing this is shown at (fig. 1), and is also illustrated 

 diagrammatically in fig. 2. Referring to the diagram, a and 

 b represent two levers, which are pivoted at c and d respec- 

 tively. On the right-hand end of the lever b a ball eis fixed, 

 and the weight of this is counterpoised by another ball /, 

 which rests on a rocking platform g, pivoted on the other end 

 of the lever. Opposite the end of the rocking platform g, and 

 fixed to the end of the lever a, there is another platform, h, 

 which receives the ball /when it rolls off the platform g. The 

 ball is prevented from rolling sideways by light springs, i i, 

 fixed to the sides of the platforms. On the end of the lever a, 

 or on another lever connected with it, the end of the spindle 

 of the wheel j is supported. This wheel is in gear with the 

 pinion k, which is on the shaft of the most distant of the two 

 governors from the driving-power. The ball /is so adjusted 

 over the pivot of the rocking platform g that an exceedingly 

 slight disturbance causes it to roll forward on to h, tilting g 

 over, and at the same time pushing down the end of a and 

 raising the wheel j out of gear with the pinion k, thus allowing 



