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cipated, from (a) the extreme minuteness of the actual! earth 
movement, and (b) the large discrepancies in the reports from 
different localities, both as to the time and the direction of 
the shocks. 
I have referred to the minuteness of these shocks. As the 
result of my experiments in the way of measurement I am 
satisfied that a greatly exaggerated notion of their magnitude 
generally prevails. To correct this notion, I offer a brief 
description of some of the apparatus which I have employed 
in the detection and measurement of the tremors. I at 
first tried some of the most approved forms of seismometer, 
amongst others the crossed U tubes of mercury—also a 
plate of glass, smoked on its upper surface, resting on three 
marbles, free to roll on a level glass slab. A pin point rested 
lightly on the smoked surface. This has recorded only once. 
I also tried a saucer of mercury, covered with a layer of 
treacle. Of the above, and other forms of apparatus 
unsuccessfully tried, a fuller description is given in my 
original MS. in the Society’s library. The negative evidence 
furnished. by these failures has, however, an important bearing 
upon the question. The fact that a small wooden style about 
din. in length, stocd on one end, reduced to a base of 
jig. in diameter, has been overturned by only a few of 
the strongest shocks, speaks volumes. 
It was evident that, for positive results, I must contrive 
something far more sensitive than the foregoing. 
The following apparatus, which I now employ, I have found 
fairly successful :-— ; 
For Time Signal.—A. free pendulum is suspended by copper 
wire, the end projecting below the bob and passing through a 
loop of platinum wire, this loop being only just large 
enough to allow the pendulum wire to pass through freely, 
without touching. The loop and pendulum wire each form 
part of an electric circuit. The least oscillation of the 
pendulum brings it into contact with the loop, thereby closing 
the circuit. This rigs an electric bell, and at the same 
instant breaks the current which drives an electric clock, 
thereby showing the time of shock. 
So sensitive is this apparatus, that, although fixed against 
a solid brick wall, it will respond to a moderate push against 
the wall with the hand. Of course this is affected only by 
horizontal movements. The pendulum is about 10in. in 
length. I at first tried a much longer one, about 7ft. or 8ft., 
but this seldom acted, in fact only indicated the very strongest 
tremors. 
My signal apparatus for vertical earth movement consists 
of a delicate coiled spring of great elasticity, suspending a 
small weight through which the spring wire passes, the end 
