Hector.—On Earthquakes and Wave Phenomena. 37 
First, the low, hollow sound of the concussion carried through the earth 
which has been calculated to travel, on the average, at the rate of 10,000 
feet per second. Following this, at very slightly inferior velocity, comes 
the earthquake or shock, which, in its passage underneath the ocean, causes 
what is termed the forced ocean wave, which is a slight vibration communi- 
eated vertically to the water directly over it during its progress. It is this 
forced wave that causes the concussion on board ships by which the occur- 
rence of an earthquake is recognized by mariners. 
Along the shore the forced wave causes a gentle rise of the waters for a 
short time. 
If not too distant, the sound of the concussion conveyed through the 
water of the ocean next reaches the observer, like the low, murmuring growl 
of distant thunder, followed in some cases by the sound carried through 
the air at the ordinary velocity of 1,140 feet per second. 
Last of all, and after a comparatively long interval, the great sea wave 
caused by the mechanical displacement of the waters immediately over the 
seat of the disturbances reaches the land, causing, as it approaches the shore, 
a marked and sudden retirement of the waters. According to the height of 
the original waye and the depth of water as it nears the shore, the wave, 
which may be quite unnoticed on board a ship in the offing, rises into several 
secondary waves, which advance with diminished velocity but increasing 
height, until they sweep over the low lands far beyond the reach of the 
usual tides. A series of waves of oscillation following in the train of the 
great sea wave, varying in magnitude according to the form of the coast line, 
closes the series of phenomena. 
The rapidity with which the ocean wave travels depends, of course, on 
the depth of water, but in the open sea it has been found in some cases to 
be as much as 600 feet per second (420 miles per hour). 
Although the slowest moving of the different impulses which originate 
from submarine convulsions, the oceanic waves appear to extend their 
influence to the greatest distance. In the case of the recent wave, this 
movement of the ocean was the only evidence which reached us of the 
occurrence of what will, I have little doubt, prove to have been a terrible 
convulsion in some part of the southern seas. 
From eareful consideration of the various accounts which have been 
received, it appears that the irregularity of the usual flow and ebb of the 
tide was experienced along the whole of the east coast of the islands and 
also in Foveaux Straits and Cook Straits, and that it was due to the 
influence of three distinct oceanie waves, which reached the coast from the 
eastward on the forenoon of Saturday, the 15th inst., at about the following 
periods :—First, between 3 to 4 a.m.; second, between 7 to 8 a.m. ; third, 
