Hectoe. — On 'Em'iliqiialces and Wave Phe,nomena. 37 



Pirst, the low, hollow soimd of the concussion carried through the earth 

 which has been calculated to travel, on the average, at the rate o£ 10,000 

 feet per second. EoUowing this, at very slightly inferior velocity, comes 

 the earthquake or shock, which, in its passage underneath the ocean, causes 

 what is termed ihe forced ocean wave, which is a slight vibration commiini- 

 cated 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 vt^aters. According to the height of 

 the original wave and the depth of vi^ater as it nears the shore, the wave, 

 which may be qtiite unnoticed on board a ship in the offing, rises into several 

 secondary waves, Avhich 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 sloAvest 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 careful 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 oceanic 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, 



