SES Oe tC LP Um 
ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 93 
solids. 
1 (a). 
2 (a). 
3 (a). 
4: (a). 
5 (b). 
G (b). 
7 (0). 
ment of liquids; 5. those dependent upon the partial displacements of 
Of the first elass, there have been— 
That of Cacciatore of Palermo, long in use in Sicily. It consists of a 
wooden circular dish about 10 in. ‘diameter, placed horizontally and 
filled with mercury to the brim-level of eight notches that face the 
cardinal points and the bisecting rhumbs between, and are cut down 
through the lip of the dish, equally in width and depth all round. 
Beneath each such notch a small cup is placed, to receive such mer- 
cury as may be thrown out of each notch by an oscillatory displace- 
ment of the main mass of mercury, due to a general oscillation of the 
whole system. Either the volume or the weight of mercury found in 
each cup is supposed to measure the value of the displacement, and 
hence of the shock in its direction in azimuth. 
The wooden or other bowl of molasses, or other such viscid liquid, 
suggested for use by Mr. Babbage. 
A cylindric tub with chalked or whitewashed sides, and partially 
filled with some heavy and permanently coloured liquid of deep tint. 
(Mallet, Admiralty Manual, sect. vii. p. 218.) 
Tubes partially filled with mercury, |__-shaped, with the horizontal 
and open limbs directed to the cardinal points, for the horizontal com- 
ponent of shock; and U-shaped for the vertical component,—both 
sets being provided with marking indices, to show previous displace- 
ment of the mercury. (Mallet, Admiralty Manual, sect. vii. p. 214.) 
The oldest, probably, of seismometers, long set up in Italy and southern 
Europe. A pendulum, free to move in any direction, carries below 
the bob a stile partly immersed in a stratum of dry fine sand spread 
to uniform thickness over the concave surface of a circular dish 
placed beneath, marked to the cardinal points, whose centre is 
beneath the point of suspension of the pendulum when at rest, and 
whose concavity is that of a spherical segment of a radius equal to 
the length of the. pendulum and stile, plus rather more than the 
depth of the stratum of sand. It was supposed that the stile would 
mark a right line when seen in a plane vertical to the sand-bed, and 
in the direction of the shock. 
The inverted pendulum, held vertical when at rest by its forming 
part of a spring at the base (like the watchmakers’ noddy), armed 
with a chalk tracer or pencil above the bob, marking a line or lines 
upon the concave lower surface of a dish in form like that of the 
preceding. This was understood to be one of the instruments adopted 
by the observers of the repeated shocks of Comrie, &c., and the in- 
vention, in its improved form, of Prof. J. Forbes. (Phil. Trans. Edin. 
vol. xv. part 1; Trans. Brit. Ass. 1841-42.) 
The inverted spring and ratchet pendulum seismometer, proposed in 
1854 by Robert F. Budge, Esq. of Valparaiso, in a letter (12th March 
1854) to Mr. Patterson of Belfast, and obligingly forwarded by him to 
the author. Four cylindrical or square rods of spring steel, each carry- 
ing a spherical bob (an iron shot) at top, are fixed vertically. Each is 
provided with a ratchet, finely cut upon the rod, and a pall, the planes 
of motion of the four palls passing through the cardinal points, so that 
each spring pendulum is free to make one semioscillation only in its 
own direction, or that of its ratchet and pall, and be arrested there 
by the latter until its position of displacement be observed and it be 
released. Thus, in the figure (2), p W is the spring pendulum (which, 
it may be remarked, would be better a flat ribbon of spring steel, 
