26 
horizontally, in any azimuth, through the crust and surface of 
the earth, from any centre of impulse, or from more than one, 
and which may be attended with sound and tidal waves, 
dependent upon the impulse and upon circumstances of position 
as to land and sea, This definition was illustrated by a diagram- 
matic representation of the path of a typical earthquake, and 
underneath was given a glossary of the more important terms 
connected with earthquake study, as follows:—(1) Seism—an 
earthquake ; (2) Seismology—the science of earthquakes; (8) 
Seismometers —instruments to measure the extent of the horizontal 
and vertical components of an earthquake ; (4) Seismograph— 
record of an earthquake motion traced out by a style on a 
moving smoked plate or by a spot of light on a moving roll of 
sensitive paper; (5) Seismoloques—catalogues giving details of 
all recorded earthquakes ; (6) Centrum, Focal Cairty or Origin— 
positions in earth’s crust from which the elastic waves started ; 
(7) LEpicentrum—point vertically above centrum; (8) Seismic 
Vertical—line joining origin and epicentrum ; (9) Wave Paths— 
lines radiating from focus; (10) Angle of Emergence—angle 
made by wave path and the horizon; (11) Isoseismic or Coseismic 
lines—lines of equal mechanical effect, theoretically they would 
be circles in a homogeneous medium, in reality they are irregular 
curves; (12) Meizoseismic Area—area of maximum destruction ; 
(18) Bradyseism—slow secular upheavals of earth. 
The next slide showed the earliest Seismometer, viz., 
Choko’s, a Chinese invention of a.p. 186,—really a pendulum 
instrument, arranged so that the swinging of a pendulum would 
cause a ball to move in a definite direction through a dragon’s 
mouth into that of an expectant frog’s, who gratefully acknow- 
ledged the receipt of the ball by wagging his head up and down 
for some minutes. Another slide gave diagrammatic represen- 
tations of the pendulum types of Seismometers,—(1) the long 
simple pendulum; (2) the duplex pendulum, as used by Mr. 
Gray and Professor Ewing; (3) the horizontal component 
recorder ; (4) the vertical component recorder; (5) Darwin’s 
bifilar pendulum with moving spot of light; and, lastly, Pro- 
fessor Milne’s perpetual Seismometer and recorder. 
Mr. Hora then discussed the premonitory symptoms of 
earthquakes, such as physiological effects on birds and animals, 
effects on springs, and the sea, subterranean noise, &c¢., and 
stated that though such symptoms of coming seismic activity 
were exceedingly vague, yet well authenticated prognostications 
were recorded. The effects of a typical earthquake were then 
detailed—the minute vibrations of a period of 1-5th to 1-20th 
of a second, the shock itself with a period of one or two or more 
seconds, and the after shocks ; moreover, the lecturer remarked 
that the vibrations were generally performed in different azimuths, ~ 
there being a twisting movement as well as a vertical and 
