The San Francisco call., 1897-02-07
0
Be

pense of erecting new structures for OBJ
servations. This is not regarded as neces-
sary. At most or all of the i'm portant
points WI ere observatories are desira BILE,
observatories equipped and manned al
ready exist, and all that is requisite is to
install seismographs and to instruct the
observers in their proper use.
1t is intended that the records thus
made shall be given the widest publicity
and shall be made accessible to all in
quirers. Besides being of more practical
use, they help to educate the students OF
physics and also interest and enIighten
the merely curious.
With slight smile Mr. Dunn remarked
apropos of one important phase of earth
quake observation: when we get our
smograph, 1 suppose on Sundays, Mon
days, holidays and other days when news
items are scarce, the city editor will as
sign a man to come and see if the seismo-
graph has not recorded an earth tremor.
1t is not improbable that we will have
such records oftener than might be sup
posed, because various causes occasionally
sufficiently disturb the seemingly solid
surface of this land we live in to make a
record on an instrument so delicately ad-
justed as a seismograph.
Local causes often account for move
ments OF the earth palpable enough to
startle people and terrify the ignorant and
superstitious. Explosions, landsIides and
other sudden conclusions might slightly
affect seismograph. In 1906 there was q
landslide at RosSberg, Switzerland, which
occasioned a local quaking of the ground.
Volger Mohr and other writer's on seis-
mology have suggested that some OF the
small earthquakes which have been felt
in Germany might be traced to the caving
in of the roofs of enormous subterranean
cavities gradually followed out by the
solvent action of water on deposits of rock
salt, gy psum and limestone.
The installation of seismograph would
doubtless, on general principles, be as
welcome to other observers as it would to
Mr.. Dunn. The definite purpose of Pro-
fessor Milne now is, however, to deter
mine the velocity with which motion is
communicated from an origin tbrough
our earth to its antipodes and to other
points upon its surface. From such de.
examinations of speed, which are appar.
entIv higher than we should get were our
world bali Of steel or glass, new light
would also be thrown upon its effective
rigidity, factor of Importance in many
vestigations.
The Trans-Oceanic and several subma.
rine cable companies will have a yerv
practical reason to be interested in the
work OF the new earthquake survey. Sub-
marine disturbances have often resulted
in the dlsarrangement, breaking and even
virtual destruction of cables. 1t is conf.
IDENTIFY asserted that the survey would
localize the origin of the disturbances
while at the same time light would he
thrown upon changes which are continu.
ously in operation upon the sleeper stones
! of ocean beds.
The seismome eters, with their RECORDING
| apparatus to be used in the big earthoua se
| survey, will have all the latest i'm move
ments. These instruments will no AL
the other movements besides great sud.
den displacements which recent observa,
tions have shown are characteristic n
earthquakes. The movements ciassed s.,
earthquakes resemble real EARTHQUAKES IN
| the rapidity with which they occur hnt
differ from earthquakes in being inner
ceptible until detected by instrumentor
means.
| Another class OF movements desienatac
as 'earth fittings" are manifested bv .
slow bending and unbend ng of the sur
face. Measurements OF these movemeot,
! therefore differ. The thing measured ir