The San Francisco call., 1897-02-07

, ordinary earthquakes and earth tremors is
the displacement of point in the earth's
crust. In the application OF measuring
instruments to slow "tilt1ng" the thing
measured IS any change in the plane of
the earth's surface relatively to the YER
tical.
1t is probable, therefore, that Professor
Mines plan includes the use of two seis.
mographs. The one following what is
termed the inertia method Will be an i'm
proved duplex pendulum seismograph.
This instrument draws horizontal plan
of the path pursued during an earthquake
by point of the earth's surface. 1t, how
ever, takes no note of the displacement of
time, an element that must be considered
in estimating the violence of an earth
quake from the record.
In order to ascertain the elapsed time of
the passing of the earthquake the whole
movement is resolved into rectilinear COM
ponents and these are separately recorded
on q continuously moving plate drum.
The point of the Indicator draws an undu-
lating line, from which the number, sue
cession, amplitude, velocity and acceiera-
ton OF the component movements can be
deduced and the resultant motion deter
this horizontal pendulum seismograph
which has been used to record Japanese
earthquakes for the past sixteen years.
To measure earth tremors an instrument
still more complicated and delicate than
those briefly referred to is desirable. Sew
eral bearing such names as micro
seismoscope" or 'microseismometer'' have
been invented. The desideratum in this
line of scientific invention has been to find
a mode of suspension which is at once
astatic, or superior to the influence of the
earth's magnetism, and as nearly friction
less as is possible. The crossed-line sus-
pension device as readily realizes this as
anything that has been devised up to date,
This microseismometer consists of two
bobs separately suspended at right angles
to each other, one above the other, in a
cast-iron case. To the top of the case is
fixed microscope. Its micromometer
eyepiece Is focused on a hair stretched
transversely across q vertical tube in the
upper bob. This measures horizontal
motion in the plane of the drawing,
Motion at right angles to this is shown by
the lower bob, which carries q similar
transverse hair. A lens which Is fixed
between the bobs reveals an image of the
lower hair in the plane of the upper hair,
SO that both appear crossed in the micro
scope. Both components of horizontal
motion can thus be observed together.
II is in Professor Mines scheme to
have central earthquake station in Eng
land. 1t may be either located on the Isle
Of Wight or at Greenwich. This central
station would have instruments to record
not only the slower pulsatory motions OF
the ground, but also to register the mora
rapid vibrations. To obtain complete
record of some earthquakes minor record
is required of the premonitory symptoms
eliminating in it's birth, the magnitude
and frequency of the vibrations CONSTITUTE
ing it's life, and the spasmodic tremolngs
which are seouent upon the relle1 OF the
seismic strain.
| The aggregate of the sums Annually
spent by civilized nations upon the ooser-
vation of movements IN the heavens, IN
the atmosphere and upon lnlano and
| ocean waters is enormous. nile ali THIS
| labor, study and expense goes on we our
selves and the supposititiousiy stationary
| locations of the instruments useo 10 record
| such changes are frequently moved back
and forth-in some parts OF the world
altogether for hours-durlng every year.
The people of the unlIed states, especially
those on the lower Pacific coast region,
where earth movements are frequent, and
the inhab abitants of the Carolinas, with
whom their realistic earthquake is still
living. sad and serious memory, will watch
with interest for the installation OF Pro-
fessor Mines system and his seismo-
graphs