9^ THILOSOPHICAL TRANSACTIONS. [aNNO 1666. 



ward and rise higher at the fore part of the vessel : and, contrarywise, if the 

 vessel be suddenly put forward faster than before, the water will dash backwards, 

 and rise at the hinder part of the vessel. So that an acceleration or retardation 

 of the vessel which carries it, will cause a rising of the water in one part, and a 

 falling in another; which yet, by its own weight, will again be reduced to a 

 level as it was before. And consequently, supposing the sea to be but as a 

 loose body, carried about with the earth, but not so united to it, as necessarily 

 to receive the same degree of impetus with it as its fixed parts do, the accele- 

 ration or retardation in the motion of this or that part of the earth will cause 

 such a dashing of the water, or rising at one part with a falling at another, as 

 what we call the flux and reflux of the sea. 



Now, this premised, we are next, with him, to suppose the earth carried 

 about with a double motion ; the one annual, as (Fig. 1. pi. 3.) in BEC the 

 great orb in which the centre of the earth B is supposed to move about the 

 sun A. The other diurnal, whereby the whole moves upon its own axis, and 

 each point in its surface describes a circle, as D E F G. 



It is then manifest, that if we suppose that the earth moved but by any one 

 of these motions, and that regularly, the water having once attained an equal 

 impetus thereunto, would still hold equal pace with it ; but the true motion of 

 each part of the earth's surface being compounded of those two motions, the 

 annual and diurnal ; while a point in the earth's surface moves about its centre 

 B, from G to D and E, and at the same time its centre B be carried forwards 

 to C, the true motion of that point forwards is made up of both those mo- 

 tions ; to wit, of B to C, and of G to E ; but while G moves by D to E, E 

 moves backward by F to G, contrary to the motion of B to C ; so that the 

 true motion of E is but the difference of B C and E G ; for beside the motion 

 of B about the centre, G is also put forward as much as from G to E, and E 

 put backward as much as from E to G ; so that the diurnal motion in that 

 part of the earth which is next the sun, as E F G, abates the progress of the 

 annual, and most of all at F ; and in the other part which is from the sun, as 

 GDE, it increases it, and most of all at D, that is, in the day time there is 

 abated, and in the night time added to the annual motion, about as much as is 

 G E, the earth's diameter. Which would afford us a cause of two tides in 

 twenty-four hours ; the one upon the greatest acceleration of motion^ the 

 other upon its greatest retardation. 



And thus far Galilaeo's discourse holds well enough ; but then in this it comes 

 short, that as it gives an account of two tides, so those two tides are always 

 to be at F and D, that is at noon and midnight ; whereas experience tells us 

 that the time of tides moves in a month's space through all the 24 hours. Of 



