268 PROCEEDINGS OF SECTION A. 
No. 13.—THE SOURCE OF THE PERIODIC WAVES 
WHICH ARE RECORDED FROM TIME TO TIME 
ON THE SYDNEY AND NEWCASTLE TIDE- 
GAUGES. 
By H. C. Russetz, C.M.G., F.R.S., F.R.A.S., de. 
(Read January 11, 1898.) 
[ Abstract. | 
A.most from the first day the Sydney and Newcastle self-recording 
tide-gauges were established—the former in 1867, the latter in 
1871—LI have found on the daily record sheets from time to time 
periodic waves recorded with the tidal curves. The period is 
usually about twenty-six minutes. In 1868 we were surprised 
by the records of waves of unusual dimensions, some of which 
caused a rise and fall in Sydney harbour of 3 ft. 6 in. These 
waves continued to reach our coast and record themselves for 
four days, z.e., August 15, 16, 17, and 18. Such an unusual 
display indicated unusual energy somewhere, and the waves were 
soon explained by the news of the great earthquake at Arica, 
in South America. One account, given to me by Captain 
Conlon, who was passing Arica at the time, throws some light 
upon the character of the waves. He was then the captain of a 
large steamer running from London to San Francisco, and was 
passing Arica at the time of the earthquake. ‘The shocks,” he 
said, ‘‘ were extremely violent, and everything that was breakable 
in the steamer, even to the binnacle lamps, was thrown down and 
broken. It felt as if the steamer was struck violent blows from 
below, which made her shiver from end to end as if she was going 
to pieces.” From the shore mighty waves rolled away towards 
Australia across the Pacific Ocean at the rate of 360 miles per 
hour. At Sandwich Islands they were still 40 ft. high, and at 
New Zealand they were 6 ft. and in Sydney, as stated above, 
3 ft. 6 in. 
In 1874 and 1877 and other years we have had similar waves, 
and I have been able to trace them to reported earthquakes ; and 
in the intervals between these larger disturbances we have had 
recorded frequently periodic waves of the same character but 
much less amplitude. At first these were credited to unknown 
earthquakes, but from time to time instances occurred when 
earthquakes took place and there were no periodic waves. Some 
of these were evidently due to great storms in Tasman Sea, but 
