iEleport of Committee No. Z. 



THE TIDES OF THE COAST OF SOUTH 

 AUSTRALIA. 



Members of Committee. — Professor Bragg, Captain Inglis, Professor 

 Lyle, Mr, R. W. Chapman (Secretary). 



Very little work has been done so far in the way of investi- 

 gating the nature of the tides along the Australian Coasts, 

 although the records shew many peculiar and interesting 

 features. The only analysis we believe yet done in this 

 direction was performed by Sir W. Thomson and published 

 in a communication to the British Association in 1878 ; this 

 was an investigation of the results of tidal observations made 

 at Fremantle, W.A., by the Officers of the Admiralty Survey. 

 This Committee since its appointment has been at work 

 upon the records of South Australian tides as recorded by 

 three tide-gauges established at Port Adelaide, Port Pirie, 

 and Port Augusta. The records from the three gauges 

 exhibit the same general features. There is the usual regular 

 semi-diurnal tide, with a well marked diurnal inequality ; 

 this inequality changes some time before the first equinox 

 and some time after the second ; that is to say, before about the 

 middle ojf February the morning tide is the higher, but after 

 that, until about the middle of October, the afternoon tide is 

 higher than the morning tide. But the most characteristic 

 feature is what is locally termed the " dodging-tide," which 

 takes place regularly at the neaps ; at this period, for a 

 varying interval of about 24 hours, there is no tide at all in 

 the usual acceptation of the term, and the tide-gauge shews 

 an almost straight line, and in all cases the nature of the 

 curve at this time is markedly different from all the rest. 

 For a short time both before and after this also the tide is 

 irregular both as regards time and height. We selected the 

 records from Port Adelaide as being probably the most 

 reliably kept, and these have been subjected to Harmonic 

 Analysis by Captain Inglis and the Secretary. The analysis 

 has been performed by the method elaborated by the 

 Committee of the British Association, and the results are 



