VOL. XIII.] PHILOSOPHICAL TRANSACTIONS. 955 



A correct Tide Table, showing the true Times of the High-waters at London 

 Bridge, to every Day in the Year l683. By Mr. Flamsteed. N" 143, p. 10. 



An Account of the Tide-table. — Considering how much the river Thames is 

 frequented by shipping, and how long it has been the chief place of commerce 

 in these parts of the world, our seamen's accounts of its tides should be very ex- 

 act, and their opinions concerning them rational; whereas if they be inquired 

 into, nothing will be found more erroneous and idle. For, observing that the 

 high-waters at and near the new and full moons, run an hour and a half, or 2 

 points of the compass, longer than at the quarters, they conclude generally that 

 it is the variable winds that cause it, never considering how improbable it is that 

 so inconstant and changeable a cause should effect so constant an inequality. 



In which opinion the tide tables of our almanacs have contributed much to 

 confirm them; for there the moon's age is got by the epacts; thence the time 

 of her southing, by the allowance of 48 minutes of time for every day's age, 

 as if her diurnal motions and returns to the meridian were altogether equable, 

 than which nothing is more false; and then the time of the high-water at 

 London bridge is made by adding 3 hours to the time of her southing so 

 gotten, as if there were the same constant space of time between the moon's 

 southing and the high-waters, which by this means are often made 2 hours dif- 

 ferent from truth and experience. 



To amend this fault, some of the more skilful have calculated the times of 

 the moon's southings exactly, and then made their tide tables by adding 3 hours 

 constantly to them; by which means, though they agreed nearer with experi- 

 ence at the spring-tides, or near the new and full moon, yet they erred not 

 much less than by the old way at the quarters, or in the neap tides ; the ine- 

 quality of the tides being above double to the error committed in finding the 

 moon's southings by her age. 



Mr. Booker, in his almanac, was the first that gave any directions for the 

 amendment of this reckoning, and that was only to subtract an hour from the 

 times in his tide-table, about the first and last quarters of the moon, because 

 the neap-tides did not flow so long as the springs by 1 point of the compass. 

 But Mr. Henry Philips, a person well known by his works of navigation, was 

 certainly the first that brought the inequality to a rule, whose Theory of the 

 Tides, and a table grounded on it, for the year l668, was printed in Mr. Ol- 

 denburg's Philosophical Transactions, for the month of April that year, N° 34, 

 which was found much more conformable to experience than was expected. 



Having frequent occasion to pass between London and Greenwich by water, 

 some 2 years ago I observed that the tides seldom hold out so long as Mr. 



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