108 Mr. Mauer on Earthquake Registration Instruments. 
of a column of mercury, in two vertical and four horizontal glass tubes, of pecu- 
liar construction. One end of the column of mercury, in each tube, is so adjusted 
just in contact with one pole of a constant galvanic battery, that the oscillation 
produced in the mercurial column by the wave, in passing, breaks contact. ‘The 
time during which the contact remains broken is proportionate to the amount of 
the vertical and horizontal elements of the wave. The breach of contact releases 
one or more of six pencils at the instant of its occurrence, and, until contact is 
restored, either of these continues to describe a trace upon a ruled sheet, placed 
upon a cylindrical barrel, which is carried round by the astronomical clock. The 
length of this trace is, therefore, a graphic representation of the amount of the 
respective element of the wave, and the pencil which marks it indicates the 
direction of the oscillation, whether vertically positive or negative, or horizontally 
from any point of the compass. 
The velocity of wave transit is constant for each instrument, inasmuch as it 
is constant for any given formation upon which the instrument may be estab- 
lished ; hence the time of broken contact is not perplexed by any consideration 
of the velocity of the wave. 
A somewhat similar arrangement marks, upon each of four dials, the hour, 
minute, second, and fraction of a second, at which the crest of the wave has passed 
the point of the observatory, or locus of the instrument. This is of peculiar 
importance, in order to ascertain the rate of progress of the wave between two 
distant observatories. 
The instrument will continue to register by itself for twelve hours at a time, 
and at such an interval its registrations require to be read off and noted. 
It is capable of registering waves of vertical or highly inclined transit, as well 
as those whose motion of translation is horizontal; but in places where waves of 
both orders may be expected to occur simultaneously, certain additions will be 
necessary, in order subsequently to distinguish the recorded elements of each 
system of waves. 
