52 Professor Barlow on the Tides 



viz. by subtracting from the depth of water on one side, the 

 depth on the other. Thus it appears that, on the day in ques- 

 tion, 



The above deductions are from the observations of a particu- 

 lar day, and are not quite the mean results even for a day, be- 

 cause the high water above and below bridge does not happen 

 exactly at the same time. From a mean, however, of several 

 days, it appears, that the average fall 



Feet. Inches. Feet. Inche*. 



High water spring tide is 8 greatest 1 1 



Average faU low water 1 ^ ^ ^^^^^^^ ^ ^ 



Do. J 



High water neap-tides 5 



Low water do. 2 1 least 1 1 



3. Some other particulars relative to the periods of Rise and 

 Fall, and of High and Low Water, above and below Bridge, 

 may be stated as follows : 



1. The flood of spring- tides, of October 21st and 23d, pro- 

 duced slack water through the bridge in about 40 minutes after 

 low water below bridge ; from which time a-head gradually in- 

 creased below bridge to 1 foot 10 inches at half flood, and then 

 regularly decreased to about 8 inches at high water. 



The first flow of these tides, nevertheless, began above bridge 

 about 20 minutes after low water below bridge, although the 

 water was then about 2 feet 6 inches higher above than below 

 bridge; the time of low water below bridge averages 10 minutes 

 earlier than above bridge. 



