6 JOURNAL OF SCIENCE. 
while mines are the most secure places of all. The most dan- 
gerous place for a building is near an escarpment, or bank, that 
runs at right angles to the earthquake wave. Here the rock, 
whether it be solid or not, is unsupported on one side, and _ then, 
if the force of the impulse is sufficient to overcome the cohesion 
of the particles of rock, fissures will be formed and landslips will 
take place. 
All these effects can be experimentally illustrated by the row 
of billiard balls. If the balls are in close contact, and a die is 
placed on the top of each, then, when the row of balls is gently 
struck by another ball, all the dice will remain in their places ex- 
cept that on the last ball, and, perhaps, on the one next to it. 
But if there is a slight interval between each ball, then each die 
will be overthrown. The unsupported rock which fissures, or 
falls down with the earthquake shock, answers to the last ball of 
the row, which flies off when the first is struck. In every town 
subject to earthquake it is very important that accurate observa- 
tions should be made of the direction the principal waves take, 
and that cuttings should as much as possible, be made in the 
same direction. 
The second question, “ Where do earthquakes come from ?” 
that is, what is the geographical position of the centre of impulse, 
and-how deep is it situated below the surface? will require a 
different answer for each country ; and, so far as New Zealand is 
concerned, the necessary observations for settling these points . 
have not yet been commenced. The shocks on Mount Vesuvius 
are regularly recorded by Prof. Palmieri; and the occurrence of 
an earthquake in Switzerland, in December, 1879, has induced 
that scientific little country to make preparations for recording 
all future shocks. But Japan has now taken the premier position 
in earthquake enquiries. A Seismological Society was formed in 
April, 1880, “to collect and systemize facts which are in any way 
connected with earthquakes and volcanoes ;” and we learn from 
the address of Prof. Milne that valuable work has been already 
done. Fifteen seismometers, on the pendulum type, are distri- 
buted in the district round Tokio and Yokohama, in the telegraph 
offices, and these are all connected with clocks regulated by 
Tokio time, so that all the elements necessary to determine the 
position of the centre of impulse, the velocities of shock and 
transit, and the amplitude of the wave, will be recorded. Experi- 
ments have also shown that for small shocks the simple seismo- 
meters of columns of different sizes are of little use, owing to 
the mechanical difficulty of getting the base of a small column 
perfectly flat and perfectly at right angles to its axis. Heavy 
pendulums work better; but the new system of vibrating springs 
seems to promise the best results with regard to velocity and 
amplitude of shock. 
Any answer to the third question, “How are earthquakes 
caused ?” must for a long time be purely speculative, 
