Hector. — On EarthquaJces and Wave Flienomena. 41 



witli slightly abated iutensity, in five hours more. This gives the average 

 velocity at a Kttle over 290 feet per second between the Chatham Islands, 

 and 360 feet per second from New Zealand to Australia, supposing that 

 these places lie in the direct line of its progress. 



From the ratio which this shows of increased velocity and diminished 

 amplitude of the wave, a rough approximation of the distance from New 

 Zealand at which the wave originated is obtained, and indicates it at over 

 3,000 miles. If the earthshock, which originated at the same time with the 

 wave, had reached us, owing to its greater velocity it would have travelled 

 the same distance in less than half an hour, and been felt about ten hours 

 before the sea wave was observed. 



As compared with the speed at which oceanic waves have been discovered 

 to cross the Northern Pacific, this velocity is much less, and may be due to 

 the Southern Ocean having an inferior average depth. 



I may remark that if efficient means were provided for the exact observa- 

 tion of such phenomena, we should be able to arrive at the solution of very 

 important facts in physical geography, as from such waves we might deter- 

 mine the depth of the ocean and from the earthquake shock we could 

 arrive at the nature of the rocks which form its floor. It is by the latter 

 means alone that we can ever hope to learn anything of the geological 

 structure of the great proportion, amounting to nearly three-fourths, of 

 the whole surface of the earth which is covered by the waters of the sea. 



With respect to the direction in which the wave we are considering 

 appears to have travelled, the reported circumstance of its reaching Sydney 

 and Adelaide at the same time, while it does not seem to have been observed 

 at Melbourne, (most likely owing to the expanded form of the harbour, and 

 the shelter afforded by Tasmania, where it was severely felt from the south- 

 east), and lastly, its not having affected the inner parts of Auckland Harbour, 

 indicate that its course was from south of east. 



I wish further especially to call attention to the rumours that there has 

 been a recent rise of the land in this harbour, and that the tide does not now 

 rise to its proper limits ; on the other hand, that it falls lower than it formerly 

 did with the same state of the tides. This has been connected with the 

 occurrence of the ocean waves, but it is to the slight earthquake shock Avhich 

 we experienced that we must refer as the cause of the change in the level, if 

 it has really taken place. I have carefully examined many points of the 

 shore of the harbour, but have failed to satisfy myself that a change has 

 l-ecently taken place ; but the subject is one requiring further exact observa- 

 tions, extending over several periods of spring tides, before any conclusions 

 can be arrived at. 



Any elevation, however slight, occurring in such a mild manner, will 



a 



