110 Mr. Matter on Earthquake Registration Instruments. 
These bars, together with their moving gear, the mitre wheels, v, &c., are sup- 
ported by the columns d’, d”, all of which are of brass. 
The portion of the instrument at V receives the oscillation from the vertical 
element of positive or negative waves, and that at H receives the oscillation 
from the horizontal elements of the same, in whatever azimuth. 
p isa glass tube of about =; of an inch in diameter, having at top and bottom 
bulbs blown of the form shewn, and more at large, in Figs. 5 and 6. These 
bulbs are of equal capacity. The tube is so filled with boiled mercury that, 
when closed, the tube being vertical, the lower surface of the mercury shall stand 
at s, in one leg of the syphon, and the upper surface at 7, in the other leg, the 
air being compressed in the lower, and rarified in the upper, bulb, by the insistent 
column. A stout platina wire is sealed into each bulb, and so adjusted as to position 
that the extremity of that in the upper bulb shall just be in metallic contact with 
the surface of the mercurial column, as shewn more at large in Fig. 5. The platina 
wire in the lower bulb is zmmersed in the other end of the mercurial column, as in 
Fig. 6. The wire ¢, from the upper bulb, passes down through the brass column 
0, and is connected with one pole of the small, constant, galvanic battery, v, from 
the opposite pole of which a wire is carried, which, being properly insulated, is 
wound round the bar of soft iron g, first at one end, then at the other, and 
passing down at wu, is finally connected with the platina wire w, sealed into the 
lower bulb of the syphon tube p. 
Thus the bar g becomes an electro-magnet, the current passing round it, 
through the wires, and through the mercurial column in the syphon tube. 
Referring now to Fig. 4, fis the end of the traversing bar before described 
as carrying all the magnets and marking apparatus, of one of which, g is the 
soft iron bar, passing through the screw socket /, and surrounded by the helices 
K, K 5 © is part of the circumference of the large cylinder holding the ruled 
paper; / is a pencil (all the pencils are black at the V side of the cylinder, 
and red at the H side), held in an iron socket, formed in one piece with the 
armature m and with the spring 7, the position and form of which are so adjusted 
that while ever a current continues to pass round the bar g, the armature m is 
held fast in contact with the magnetic pole, and the pencil point kept out of con- 
tact with the ruled paper on the cylinder; but the instant the current ceases, the 
action of the spring 7 presses the pencil point against the paper, and continues it 
