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Sect. VII.j 



EARTHQUAKE PHENOMENA. 



mon clock. To fit it for this purpose bore two holes of a 

 quarter of an inch diameter, one through either side of 

 the clock-case, at a b, at the level of the lowest point of 

 the pendulum-bob and in the plane of it& vibration ; round 

 off the edges of these holes, and grease them. 



In the centre of a piece of fishing-line or stretched whip- 

 cord, make a loop and pass it round the screw or other 

 lower projection of the pendulum bob ; pass the two free 

 ends of the cord out, one through each of the holes in 

 the sides of the clock-case ; provide a squared log pf 

 lieavv wood of about five or six inches thick each wa 

 and from four to five feet in height ; cut both ends off 

 square, and stand the log uprigiit on one end directly 



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opposite the dial of the clock. 



Measure off equal lengths of the cord at each side of 

 the pendulum, and make fast their extremities to the 



close to the 



g, c d, 



two opposite sides of the upright lo 

 top ; bring the log backwards from the clock now,, until 

 the pendulum being at rest, both cords are drawn tight ; 

 and then advance the log two or three inches towards the 

 clock, so that the cords may be slacked down into a fes- 

 toon or bend at each side of the pendulum, and within 

 the clock-case, so that the pendulum may have room to 

 swing freely ; and very slightly w^edge the cord to keep it 

 so, through the holes in the clock-case, and from the out- 

 side ; see that the log rests firmly and upright upon a 



firm floor ; and now set the clock a-going. 



Tlie leng 



the cords, or the distance of the log from the clock in re- 

 lation to its height, must be such that if it fall towards 

 the clock it 



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hall bring the cords up tight before the 



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