[ >49 ] 
Xlf. The State of the Tides in Orkney ; by 
Mr. Murdoch Mackenzie. 
Read May z 5 . % T o Accounts of the Flux and Reflux 
* 749 - r ^ e Sea were fatisfaflory, till 
Sir Ifdac Newtons penetrating Genius deduced 
their true Caufe from the Laws of Gravitation. 
His Principles carried fuch Conviction along with 
them, and gave fuch an cafy Solution of fome of the 
mod remarkable e Phanomena J that Mankind feemed 
to imagine a thorough Knowledge of the Tides might 
be obtained from an attentive Confideration of- the 
Principles he had eftablifhed, without the Trouble 
of further Obfcrvations ; but, as he, and all Philo- 
fophers fince his Time, have confider’d only, or prin- 
cipally, the Influence of the Moon in elevating or 
deprefling the Tides; their feveral Directions, Velo- 
cities, and other AffeCtions, rcfulting from the In- 
fluence of Land, Shoals, and Winds, remain ftill as 
inexplicable, and as little known as ever. 
As a diftinCt Knowledge of thefe Things is not only 
conducive to the Advancement of Science, but would 
greatly contribute to a convenient and fafe Naviga- 
gation, it may not be unacceptable to communicate 
fuch Remarks on the Tides about the Orkney Iflands, 
as came under my Obfcrvation, while I was em- 
ployed in furveying and navigating that and other . Ad- 
jacent Places; hoping it may incite others to exptore 
the various Motions of that Element, on which luch 
a conflderable Part of the World are daily emplo)ed, 
in a more cxtenlive and accurate manner than has 
yet been done. 
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