114 PHILOSOPHICAL TRANSACTIONS. [aNNO 1666. 



consequently the degrees of the risings and fallings of the same in equal spaces 

 of time, are performed according to the proportion of sines. 



But it is conceived that the said proportion cannot hold exactly and precisely 

 in regard of the inequalities that happen in the periods of the tides, which are 

 commonly observed and believed to follow certain positions of the moon in re- 

 spect of the equinox, which are known not to keep a precise and constant 

 course ; so that there not intervening equal portions of time between one new 

 moon and another, the moon's return to the same meridian cannot be always 

 performed in the same time ; and consequently there must be a like variation of 

 the tides in the velocity, and in the risings and fallings of the tides, as to equal 

 spaces of time. And the tides from new moon to new moon being not always 

 the same in number, as sometimes but 57, sometimes 58, and sometimes 59, 

 without any certain order of succession, this is another evidence of the difficulty 

 of reducing this to any great exactness. Yet it is very desirable that observa- 

 tions be constantly made of all these particulars for some months and even 

 years together. And because such observations will be the more easily and 

 exactly made where the tides rise highest, it is presumed, that a fit apparatus 

 being made for the purpose, they may be made about Bristol or Chepstow 

 best of any places in England, because the tides are said thereabouts to rise to 

 10 or 12 fathoms; as upon the coast of Brittany in France, they do to 13 

 and 14. 



In order to which this following apparatus is proposed to be made use of. In 

 spme convenient place upon a wall, rock, or bridge, &c. let there be an obser- 

 vatory, standing as near as may be to the brink of the sea or upon some wall ; 

 and if it cannot be well placed just where the low water is, there may be a chan- 

 nel cut from the low water to the bottom of the wall, rock, &c. The observa- 

 tory to be raised above the high water 18 or 20 feet ; and a pump placed per- 

 pendicularly by the wall, reaching above the high water as high as conveniently 

 may be. Upon the top of the pump a pulley to be fastened, for letting down 

 into the pump a piece of floating wood, which, as the water comes in, may rise 

 and fall with it. And because the rising and falling of the water amounts to 60 

 or 70 feet, the counterpoise of the weight that goes into the pump to hang 

 upon as many pulleys as may serve to make it rise and fall within the space by 

 which the height of the pump exceeds the height of the water; and because by 

 this means the counterpoise will rise and fall slower, and consequently by less 

 proportions than the weight itself, the first pulley may have upon it a wheel or 

 two to turn indexes at any proportion required, so as to give the minute parts 

 of the motion, and degrees of risings and fallings. All which is to be observed 

 by pendulum watches that have minutes and seconds. 



