146 Transactions. 



Art. XXI. — On the Wave Phenomena observed in Lyttelton Harlour, 15th 

 August, 1868. By Captain Fred. D. GtIBSOK, Chief Harbour Master. 



[Read lefore the Philosophical Institute of Canterbury, 9th Septemier, 1868.] 



The evening of tte 14tli August was calm and clear, tlie aneroid stood 

 29"90. An unusual stillness prevailed during the night. 



At 3.30 a.m., the tide being half-ebb, the water suddenly receded from 

 the harbour, rushing past the shipping lying in the stream, and vessels 

 anchored near the entrance of the harbour, at a supposed velocity of twelve 

 knots. The water continued falling until 4.30 a.m., when the end of the 

 breakwater was dry, at which position the average depth at low water is 15 

 feet. At the before-mentioned hour, with a loud roar, a wave of about 

 8 feet in height rushed up the harbour with great velocity, and at 4.50 the 

 water was within 3 feet of the railway level ; in other words, 3 feet above 

 the highest spring tide, having risen 25 feet perpendicular in twenty minutes. 



The water at about 5 a.m. rapidly receded the second time, and at 6 the 

 bottom was again visible beyond the end of the Grovernment jetty ; at 7"15 

 it again rushed up in the form of a heavy ground swell, and rose rapidly to 

 16 feet, and immediately commenced to fall again. At 9.30 the inner end of 

 the screw-pile jetty was dry, when the reaction again took place, the water 

 returning with even more velocity than at 7 a.m., until it resumed the level 

 of high-water springs. Off in the stream, the water was very thick and 

 discoloured, boiling up as it were from the bottom. 



At 10.15 the water rushed out with the same force for about half an hour, 

 and rose again shortly after 11 a.m. to 18 feet ; throughout the remainder 

 of the day the water rose and fell without any regularity, sometimes at the 

 rate of 3 feet per hour. Aneroid, 30'5. 



During the whole of Sunday, the 16th, there was no regularity of tide, 

 the water ebbed and flowed three times in six hours ; at 2.16 p.m., the proper 

 time of high water, there was 17^ feet, and after ebbing an hour, it rose 

 again to about 17 feet at 4,15. 



Aneroid, 30" 10, stationary; weather calm and clear; water very thick, 

 and continuing to boil up in large eddies. 



Monday and Tuesday, the l7th and 18th, tides still very irregular, flowing 

 one foot higher, and ebbing one foot and a half lower than the usual springs, 



Wednesday, 19th, nothing unusual perceptible. 



