q 
a 
a 
ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA, 45 
2 (a). 
was read to the Royal Irish Academy in June 1846 (Trans. R. I. A., 
xxi. p. 107). It consists essentially of five fluid pendula,—glass tubes, 
partially filled with mercury, four for horizontal, and one for vertical 
elements of the shock. ‘The displacement of the mercurial columns 
breaks contact, in an otherwise closed galvanic circuit, which, acting 
upon some simple contrivances, cause a pencil to trace a line upon 
ruled paper, whose length is proportionate to the time that contact 
remains broken, or to the amplitude and altitude of the earth-wave. 
The ruled paper, placed upon a cylinder, is maintained in motion 
by a clock; the position of the commencement of the pencil line 
traced on the moving paper, therefore, gives the moment in time, of 
the arrival of the wave, or initial instant of shock. The displace- 
ment of the mercurial columns is dependent upon inertia, and on 
‘the relative mass of mercury in the adjacent limbs of each bent 
tube. 
Professor Palmieri, of Naples, has, some time since, constructed an 
instrument, in point of general principle, very similar to the pre- 
ceding, and which has been at work, as he informs me, with satis- 
factory results, at the Royal Meteorological Observatory upon Vesu- 
vius, and for a considerable period. His instrument consists of two 
distinct systems, one for vertical, the other for horizontal, or rather 
undulatory movements. The former consists of a clock, constantly 
going, and registering date and time. A galvanic circuit, which 
includes an electro-magnet, remains always unelosed, except at the 
instant of the arrival of a vertical movement of the whole instrument, 
when one pole of copper or platinum wire, held suspended from a heavy 
bob at the lower end of a spiral spring—as in 9 (8), last sentence— 
close over the surface of a mercurial cup (the other pole), drops by 
inertia, and making good the contact, establishes the electro-magnet’s 
action, and by it stops the clock and rings a bell. The range of ver- 
tical movement is, J believe, deduced from the direct motion of this 
contact-maker. 
The system for horizontal (?) or undulatory movements consists of 
a similar clock and galvanic arrangement, and of four U-shaped 
glass tubes, open at both ends, and containing equal vertical columns 
of mercury, The vertical planes of two of these U-tubes are N. and 
S. and E. and W.; those of the other two in intermediate rhumbs. 
Close above, but not in contact with, the mercurial surface in one 
limb of each tube, is held suspended a platinum pole, the mercury 
itself being the other pole of the open circuit. Upon the surface of 
the mercury in the opposite limb a small float rests, connected by a 
silk cord over a pulley in a vertical plane, with a little counterpoise, 
slightly heavier than the float. If, now, such a movement be given 
to any one or more of these U-tubes as shall kant it over or throw it 
out of plumb, and so alter the relative levels of the opposite surfaces 
of mercury in the two limbs of the tube, the U-tube that shall in- 
cline towards the limb that contains the platinum galvanic pole will 
then make contact, and at the moment of doing so will stop the clock 
and ring a bell as before. 
The amount of displacement as to level of the two surfaces of 
mercury in the opposite limbs will be made observable by the 
distance to which the small float shall be found elevated above the 
surface of the mercury in the opposite limb. ‘A description of this 
instrument has been given, but without a figure, in De la Rive’s 
