472 0. G. Rockwood, Jr.—Japanese Seismology. 
apparatus used in connection with this, as must also the vertical 
component. 
Another device for obtaining a magnified record of the earth- 
motion is Gray’s Rolling Sphere.* This consists of a heavy 
lead or iron sphere resting in neutral equilibrium upon a level 
plane, and therefore free to roll in any direction. Above the 
sphere an indicating lever is supported in a vertical position, 
by a sort of spring universal joint, so that its lower extremity, 
the shorter arm of the lever, engages with a hole in the highest 
part of the sphere, while its upper and longer arm carries the 
recording style. e method of arranging the fulcrum of this 
lever is peculiar. The light rod forming the lever passes cen- 
trally through a small disk to which it is fastened. This disk 
plays within a horizontal ring, from which it is supported, 
through the medium of four bent springs, which are attached 
by one end to symmetrical points on the ring and by the other 
to the edge of the disk. ‘The lever has a small weight on its 
lower arm sufficient to bring the center of gravity below the 
fulerum and to make its normal rate of vibration slower than 
that of the earthquake. The lever supported in this way is, 
by the elasticity of the springs, free to move in any direction 
as influenced by the motion of the heavy sphere. 
Gray’s Double Bracket Seismograph + also gives a magnified 
record of the actual motion of an earth-particle. This consists 
of a post planted firmly in the ground, to which is hinged, by 
its longer side, a light but strong frame, something like a gate, 
measuring Xx centimeters. e upper hinge is a knife 
edge in a ring, while the lower is a point resting in a conical 
socket. To the outer edge of this frame is hinged in the same 
way another similar but somewhat lighter one, loaded on ts 
outer part by a thick metal disk of considerable weight, which 
by virtue of its inertia forms the stationary point of the seismo- 
graph. When ready for use the planes of these two brackets 
are placed at right angles to each other, and each makes an 
angle of forty-five degrees with the face of the post. The 
record is made through the medium of an indicating lever sim- 
ilar to that above described with the rolling sphere, and sup- 
ported below the center of the heavy disk by an arm extending 
out from the post. 
Gray’s Pendulumt Seismometer aims to record the earth- 
uake motion by means of its components in three directions at 
angles of 120°. It consists of a heavy weight hanging by a 
cord three feet long, from the middle of a stretched wire. Itis 
*On Instruments for Measuring and Recording Earthquake Motions. London 
Phil. Mag., V, vol. xii, p. 199, Sept., 1881. 
London Phil. Mag., V, vol. xii, Sept., 1881. 
| ansedtions of Seismolog. Soc. of Japan, vol. i, part I, p. 44; also Lond. 
Phil. Mag., V, vol. xii, Sept., 1881. 
