112 Mr. Mauer on Earthquake Registration Instruments. 
the direction of shock is at any intermediate point, contact is broken in two tubes 
at once, as, for example, in N and E; and the direction of the wave motion is got 
by taking the resultant of the two motions, as read off from the cylinder paper. 
The wires from the upper bulbs, ¢, €’, ¢’, e’’, and from the lower ones, % ¢'5 7, ¢ 
are connected with the battery «, and with the four separate sets of marking mag- 
nets, of which two are seen at 7’, /’”, in Fig. 2, precisely in the way before de- 
scribed,—all the wires are for convenience twisted together, as there shewn, 
although individually insulated. 
The horizontal elements of North and South waves are marked, the former 
in red, the latter in black, on the column B’/BC’ of the ruled sheet, Fig. 7, and 
those of the East and West waves in black on the column B’ B’C” of the same. 
It is obvious that the ordinate AB on the ruled paper, is that of time, and the 
ordinate AC, or the circumferential motion of the cylinder, that which corres- 
ponds to the dimension and direction of the wave. 
The place in which a pencil mark occurs on the ruled sheet, with reference 
to AB, BB, or B’B”, therefore, roughly determines the time of the shock or wave 
transit ; but it is essential to know this epoch with minute accuracy. Four brass 
dials are therefore connected with the astronomical clock, two of which, p and a, 
are shewn in Fig. 3,—the other two being at the opposite side or at the ends of the 
case 7. These are so arranged, that one dial revolves once in twelve hours ; another, 
once in one hour; the third, once in a minute ; and the fourth, once in a second. 
To each of these is adapted a magnetic marking apparatus, precisely similar to 
those already described, Fig. 4, except that the marking instrument is a fine steel 
point, which strikes the brass, in place of a pencil point, and makes a fine dot, 
capable of being readily burnished out after observation. 
The wires from these magnets carry a current through a mercurial column 
in a single tube, much in the same way as described for the vertical element 
oscillation tubes, but+the range of oscillation of this is extremely limited, so that 
the current is instantly restored, as soon as broken. Thus, at the instant of the 
arrival of the shock, a mark is simultaneously made on each of the four dials, by 
which the time of its passage is registered to a fraction of a second of time. 
The astronomical clock is not shewn in the drawing, to avoid complexity. The 
instrument, as thus designed, is self-registering for twelve hours without atten- 
tion; it must then be examined, and the registrations, if any, read of; but no 
