PHILOSOPHICAL TRANSACTIONS. 



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VOL. III.] 



the neap-tides, it does not flow here so long by two points of the compass. 

 The water neither flows nor ebbs equal spaces in equal times ; but its velocity is 

 greatest at the beginning of the flood and ebb, and so gradually decreases till 

 high or low water. This is observed in spring-tides only, which are as here 

 set down in the following table, which I have made from my observations 01 

 our tides here. 



The Tide-Table for Quarters of Hours, 



The usual number of tides from new moon to new moon, or from the full 

 to the full, is 59. In the Severn, 20 miles above Bristol, near Newnham, 

 160 miles from the river's mouth (Lundy,) the head of the flood, in spring- 

 tides, rises in height like a wall near nine feet high, and so runs for many 

 miles together, covering at once all the shoals which were dry before ; at which 

 time all vessels that lie in the way of these head tides, or boars, as they are po- 

 pularly called, are commonly overset, or carried upon the banks ; and the head 

 of the tide being past, such vessels are left dry again. It flows there but 2 

 hours and 1 8 feet in height, and it ebbs ten hours. The reason of the said 

 boar is doubtless the straightening and shoaling of the river in that place, it 

 being there but half a mile broad; as it is but 20 perches over three miles 

 higher, running tapering to Gloucester. 



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