AND OTHER WATER WAVES 253 



the curve presenting " notches." These are a 

 marked and disturbing feature of the records of 

 tide-gauges, and positions are consequently chosen 

 for their erection on the coasts where the uninter- 

 rupted run of the tide shall cause them to be as 

 slight as possible. This pulsative rise of the tide 

 is sometimes strikingly visible to the eye in situa- 

 tions where there is a considerable inflow over 

 nearly flat sands. Thus, on the Anat sand-bank, 

 on the left shore of the river mouth at Montrose, 

 N.B., where I was standing at the turn of the 

 tide on March 17, 1900, the water came suddenly 

 rushing in, filling up the hollows and threatening 

 to cover the whole area. The rush, however, soon 

 ceased, and the water then receded, leaving the 

 sands bare once more ; but only for one or two 

 minutes, when another rush again occurred, and I 

 do not think that the water subsequently retired. 

 In subsequent observations on the Severn and 

 elsewhere it will be well to look out for this pro- 

 cess, especially at places below the point of starting 

 of the regular bore. It may be that these con- 

 siderations help to explain the absolute suddenness 

 of rise which constitutes the bore, and which, 

 according to Sir G. H. Darwin, is not quite what 

 is indicated by theory that is to say, by the theory 

 which regards the bore as the face of the tide -wave 

 considered as a whole. 



