A Letter mitten to Dr. John Wallis (j Mr. Henry Philips, 
containing his observations about the True 
Time of the Tides. 
WOrthy Sir, Being defired by Mr. o. to give in , what 
informations I could, concerning the Tides , I have 
made bold to prefent this Paper to your Coofideration which 
though it have little or no relation to your more cuiious Philo- 
fophical Experiments, yet, I hope, will be of very good ufe for the 
finding out the True time of the Tides at all times of the Moone ^ 
which is (I conceive) of as great concernment, as any thing in 
the Motion of the Tides. 
For, this time of the Tides, though it be a very neceffary 
thing to be known, yet is very rudely and (lightly reckoned up 
by moft Seamen and Aftronomers moftof them reckoning, as 
if the Moone being upon fuch a fct point of the Compare (as 
the Seaman calls iQor fo many houres part the Meridian^ the 
Almanack- Makers reckon ) it were High-Tide in fuch and fuch a 
Port at all times of the Moone, And thus they reckon the 
Tides every day to differ conftantly 48 m. As for inftance, A 
South-Weft Moone makes a full Tide at London > that rauft be un- 
derftood, that it is High-Tide at London when the Moon is three 
hours paft the Meridian. Now this is true indeed at the New 
and full Moon, but not at other times of the Moone, which few 
take any notice of: only Mr. Booker had wont to give this Ca- 
veat ^ that about the /?r/? and lap quarters of the Moone, the 
Neap-tides did not flow folong as the Spring-tides by one point 
of the Compajfe; but he gives no rule to proportion the diffe- 
rence. 
But obfetving this more narrowly, I find, that at London the 
Tides fall out at the leaft two points, that is., one hour and an half 
fooner, in the Quarters . then in the New and Full Moone. Now 
this being a very considerable difference of time, which might 
very well make many Seamen and Paffengers tolofe their Tides, 
I fet my felf to watch this difference of the time of the Tides , 
and to find out fome Rule, how to proportion the time of the 
Tides between the Spring-tides and the Neap-tides, and I found 
by many trialls, that xht true time of the tides might be found 
out 
