between Fairleigh and the North Foreland. 231 
proof of what I have before advanced, " that local circum- 
stances will always have an effect upon the tides, to which no 
general reasoning can apply, in all straits and insular situa- 
tions.” These circumstances, however, may readily be acer- 
tained by observation and by observation only. 
J. ANDERSON. Capt. R.N. 
36 Hans Place, 6th February, 1819. 
I have annexed a table showing the gradual rising and 
falling of the tides in Boulogne Bay, from soundings* taken 
every haif hour whilst laying at anchor there, and which I 
think will greatly tend to confirm what I have advanced, with 
respect both to the rise and setting of the tides in the Straits 
of Dover, with the times of high and low water, and of the 
change of the current of tide there ; circumstances which, 
I have reason to fear, have not been hitherto sufficiently at- 
tended to ; but which would prove of the utmost importance, 
especially on expeditions where much boat service must be 
had recourse to ; and in disembarking troops at a particular 
point, or in making an attack upon vessels at anchor during 
the darkness of the night ; when a want of the necessary 
knowledge of the tides, or as it has often been called “ a mis- 
take in reckoning them,” might be productive of the most 
fatal consequences.-f 
* As these soundings were taken with a common lead and line, and by different 
hands, I cannot venture to say that they were taken very accurately ; and there might 
also be some irregularities in the ground, which would occasion a difference ; and be- 
sides, they were taken 6 or 7 miles from the shore, where the tides do not rise quite 
so high as on the shore, owing to the re-action of the ground. 
f A mistake in calculating the tide at this very place is mentioned by Lord 
Nelson, as a reason why the boats sent in by him to attack the French flotilla in Bou- 
logne Bay, in 1801, did not get up with the enemy till long after the appointed time. 
