462 Transactions. — Miscellaneous. 



Beside the pendulum is a spiral spring, which forms the 

 vital part of a vertical-action seismograph, and which is 

 2ft. Gin. long when stretched. This descends from the top of 

 the frame beside the pendulum, and terminates on a lever at 

 about 3in. from its fulcrum. This lever is made forked, and 

 provided with two parallel fulcrums so that it cannot swing 

 from side to side — as it would if not so provided — but only rise 

 and fall ; after passing the point at which it receives the spring 

 it is carried out 3ft., when it is met by the short end of a bent 

 lever, the fulcrum of which is carried by two arms coming 

 out from the uprights of the stand.* Situated on top of the 

 forked lever, near its junction with the bent lever, is a lead 

 weight with a glass plate suspended from it, on which work 

 friction-screws. The long end of the bent lever carries a 

 needle, and marks on another glass plate. 



Besides the pendulum for recording horizontal motion, 

 there are a pair of bracket seismographs working at right- 

 angles to each other. They are made as follows : A piece of 

 wood, which must be substantial and about Sin. high, with a 

 piece projecting 2iin. from top and bottom, carries a steel 

 rod, both ends of which are held in place by steel bearings. 

 Standing out from this about Sin. is another framework to 

 carry a column of lead measuring Gin. high and 2in. in dia- 

 meter. To the bottom of the lead is fixed an indicator 2ft. 

 long, with a place at its end to carry a needle. This will 

 record on the same plate that the vertical action is recorded 

 upon. 



To receive all these records, and to give the exact time of 

 the shock, I have designed that two glass plates should be used 

 — the one, 1ft. in diameter, under the pendulum, to receive a 

 condensed record with small amount of magnification, turning 

 round once in twenty-four hours ; the other, 3ft. in diameter, 

 turning once in the hour, to receive the record from the ver- 

 tical action and the duplex-bracket seismograph. 



To economize space I intend that the small j)late shall be 

 put as far under the pendulum as possible, and the large one 

 allowed to go under it, or over, as far as will be allowed by 

 the bearing of the small plate, or the indicator of the pendu- 

 lum. The large plate will be supported from the front of the 

 stand which is carried out at each side to give the ground- 

 work for the brackets, the two indicators of which will reach 

 out away from the pendulum, and record on the furthest part 

 of the plate from it. 



Each of the plates is carried by a star-shaped support 

 made of thin wood, to give them stability. 



