VOL. II.] PHILOSOPHICAL TRANSACTIONS. 23^ 



the waters so strongly westwards as between the tropics, and so not strong 

 enough to overcome the eddy, which it meets with from the other motion, 

 which gives the sea a north-easterly motion, on these coasts, as to its usual 

 course. The current therefore of our seas being north-easterly, we are next to 

 consider, at what times it runs more to the north, and at what more to the east. 

 When it runs most northerly it runs up the Irish sea, and so up the Severn ; 

 when most easterly it runs straight up the channel, and so to the coast of Kent; 

 when between these, it beats against Devonshire and Cornwall, and those parts. 

 We are therefore to consider, as to the annual periods, that the annual motion 

 of the earth in the zodiac, and the diurnal in the equator, are not precisely in 

 the same direction, but make an angle of 23^ deg. at the equinoxes, but run, as 

 it were, parallel at the solstices ; and as they be nearer or farther from these 

 points, so is the inclination varied. Which several directions of motion cause 

 the compound motion of both to vary from the east and west more or less, ac- 

 cording as the sun's position is farther from or nearer to the solstices. And 

 therefore, nearer to the equinoxes, this inclination casts the constant current of 

 our seas more to the north and south ; and further from it, more to the east and 

 west. Which is the reason why the current up the Irish sea is nearer to the 

 equinoxes at the beginning of March and end of September, and up the Chan- 

 nel or narrow seas, farther from it, at the beginning of February and of No- 

 vember; and against the coasts of Devonshire and thereabout, at some inter 

 mediate time. 



Time of the Tides observed at London. Addressed to Dr. IFallis. 

 By Mr. Henry Philips. N" 34, p. 656. 



The true time of the tides is very rudely and slightly estimated by most sea- 

 men and astronomers; most of them reckoning as if the moon being upon such 

 a set point of the compass as the seaman calls it, or so many hours past the 

 meridian as the almanack makers reckon, it were high tide in such and such a 

 port at all times of the moon. And thus they reckon the tides every day to 

 differ constantly 48m. As for instance: A south-west moon makes a full tide 

 at London, that must be understood, that it is high tide at London when the 

 moon is three hours past the meridian. Now this is true indeed at the new and 

 full moon, but not at other times of the moon, which few take any notice of. 

 But observing this more narrowly, I find that at London the tides fall out at 

 the least two points, that is one hour and a half, sooner in the quarters, than in 

 the new and full moon. Now this being a very considerable difference of time, 

 which might very well make many seamen and passengers to lose their tides, I 



♦ Omitted here a letter from Dr. Wallis, pointing out a mistake in a book, viz. Specimena Mathe- 

 matical by Franciscus Du Laurens. 



