Selected quad for the lemma: cause_n
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B03739
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May it please the King's most excellent Majesty
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Halley, Edmond, 1656-1742.
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1687
(1687)
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Wing H451A; ESTC R177810
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7,193
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14
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May it Please THE KING' 's MOST EXCELLENT MAJESTY I Could not have presumed to approach your Majesties Royall Presence with a Book of this Nature had I not been assured that when the weighty Affairs of your Government permit it your Majesty has frequently shewn your self enclined to favour Mechanical and Philosophical Discoveries And I may be bold to say that if ever Book was worthy the favourable acceptance of a Prince this wherein so many and so great Discoveries concerning the constitution of the Visible World are made out and put past dispute must needs be grateful to your Majesty especially being the Labours of a worthy Subject of your own and a Member of that Royall Society founded by your late Royall Brother for the advancement of Natural Knowledge and which now Flourishes â—nder your Majesties most Gracious Protection But being sensible of the little Leisure which Care of the Publick leaves to Princes I believed it necessary to present with the Book a short Extract of the Matters conteined together with a Specimen thereof in the genuine Solution of the Cause of the Tides in the Ocean a thing frequently attempted but till now without success Whereby your Majesty may judge of the rest of the performances of the Author The sole Principle upon which this Author proceeds to explain most of the great and surprising appearances of Nature is no other than that of Gravity whereby in the Earth all Bodies have a tendency towards its Center as is most evident and from undoubted Arguments it s proved that there is such a Gravitation towards the Centers of the Sun Moon and all the Planets From this principle as a necessary consequence follows the Sphaerical Figure of the Earth and Sea and of all the other Caelestial Bodies and tho' the tenacity and firmness of the Solid Parts support the inequalities of the Land above the level yet the Fluids pressing equally and easily yeilding to each other soon restore the Aequilibrium if disturbed and maintain the exact Figure of the Globe Now this force of Descent of Bodies towards the Center is not in all places alike but is still less and less as the distance from the Center encreases and in this Book it is demonstrated that this force decreases as the Square of the distance increases that is the weight of Bodies and the force of their Fall is less in parts more removed from the Center in the proportion of the squares of the distance So as for Example a Tun weight on the surface of the Earth if it were raised to the height of 4000 miles which I suppose the semidiameter of the Earth would weigh but ¼ of a Tun or 5 hundred weight if to 12000 miles or 3 semidiameters from the surface that is 4 from the center it would weigh but 1 16 part of the weight on the surface or a hundred and quarter So that it would be as easy for the strength of a man at that height to carry a Tun weight as here to carry a hundred and quarter And in the same proportion does the Velocities of the fall of Bodies decrease for whereas on the surface of the Earth all things fall 16 foot in a second at one semidiameter above this fall is but 4 foot and at 3 semidiameters or 4 from the center it is but 1 16 of the fall at the surface or but one foot in a second and at greater distances both weight and fall become very small but yet at all given distances is still some thing tho' the effect become insensible At the distance of the Moon which I will suppose 60 semidiameters of the Earth 3600 pounds weigh but one pound and the fall of Bodies is but 16 3600 of a foot in a second or 16 foot in a minute that is a body so far off descends in a minute no more than the same at the surface of the Earth would do in a second of Time. As was said before the same force decreasing after the same manner is evidently found in the Sun Moon and all the Planets but more especially in the Sun whose force is prodigious becoming sensible even in the immense distance of Saturn This gives room to suspect that the force of Gravity is in the Celestial Globes proportional to the quantity of Matter in each of them and the Sun being at least ten thousand times as bigg as the Earth its Gravitation or attracting Force is found to be at least ten thousand times as much as that of the Earth acting on Bodies at the same distances This law of the decrease of Gravity being demonstratively proved and put past contradiction the Author with great Sagacity inquires into the necessary consequences of this Supposition whereby he finds the genuine cause of the several appearences in the Theory of the Moon and Planets and discovers the hitherto unknown laws of the Motion of Comets and of the Ebbing and Flowing of the Sea. Each of which are subjects that have heretofore taken up much larger Volumes but truth being uniforme and alwaies the same it is admirable to observe how easily and how satisfactorily Solutions are given in very abstruse and difficult matters when once true and genuine Principles are obtained And on the other hand it may be wondred that notwithstanding the great facility of truth and the perplexity and nonconsequences that alwaies attend erronious suppositions these great discoveries should have escaped the Acute disquisitions of the best Philosophical Heads of all past ages and be reserved to be recorded to Posterity among the Glorious Acquisitions your Nations justly promise themselves during the course of your Majesties happy Reign over us The Theory of the Motion of the primary Planets is here shewn to be nothing else but the contemplation of the Curve Lines which Bodies cast with a given velocity in a given direction and at the same time drawn towards the Sun by its gravitating Power would describe Or which is all one that the Orbs of the Planets are such Curve Lines as a shot from a Gun describes in the Air being cast according to the direction of the Piece but bent into a crooked Line by the supervening tendency towards the Earths Center And the Planets being supposed to be projected with a given force and attracted towards the Sun after the aforesaid manner are here proved to describe such Figures as answer punctually to all that the Industry of this and the last Age has observed in the Planetary Motions So that it appears that there is no need of solid Orbs and Intelligences as the Ancients imagined nor yet of Vortices or Whirlpools of the Celestial Matter as Des Cartes supposes but the whole affair is simply and Mechanicall performed upon the sole supposition of a gravitation towards the Sun which cannot be denied The Motion of Comets is here shewn to be compounded of the same Elements and not to differ from Planets but in their greater swiftness whereby overpowering the gravity that
February and October than precisely upon them is because the Sun is nearer the Earth in the Winter Months and so comes to have a greater effect in producing the Tides Hitherto we have considered such affections of the Tides as are Universal without relation to particular cases what follows from the differing Latitudes of places will be easily understood by the following figure But the motions hitherto mentioned are somewhat altered by the libration of the water whereby tho' the Action of the Luminaries should cease the Flux and Reflux of the Sea would for some time continue This conservation of the impressed motion diminishes the differences that otherwise would be between two consequent Tides and is the reason why the highest Spring-Tides are not percisely on the new and full Moons nor the Neapes on the Quarters but generally they are the third Tides after them and sometimes later All these things would regularly come to pass if the whole Earth were covered with Sea very deep but by reason of the sholeness of some places and the narrowness of the Streights by which the Tides are in many cases propagated there arises a great diversity in the effect and not to be accounted for without an exact knowledg of all the circumstances of the places as of the position of the Land and the breadth and depth of the Channels by which the Tide flows for a very slow and imperceptible motion of the whole body of the water where it is for example 2 miles deep will suffice to raise its surface 10 or 12 feet in a Tides time whereas if the same quantity of water were to be conveied upon a channel of 40 fathoms deep it would require a very great stream to effect it in so large Inlets as are the Channel of England and the German Ocean whence the Tide is found to set strongest in those places where the Sea grows narâ—owest the same quantity of water being to pass through a smaller passage this is most evident in the Streights between Portland and Cape de Hague in Normandy where the Tide runs like a sluice and it would be yet more between Dover and Calais if the Tide coming about the Island from the North did not check it And this force being once impressed upon the water continues to carry it about the level of the ordinary hight in the Ocean particularly where the water meets a direct obstacle as it is at St. Malo's and where it enters into a long channell which running far into the land grows very streight at its extremity as it is in the Severn-Sea at Chepstow and Bristol This sholeness of the Sea and the intercurrent Continents are the reason that in the open Ocean the time of high water is not at the Moons appulse to the Meridian but always some hours after it as it is observed upon all the West Coast of Europe and Africa from Ireland to the Cape of Good-Hope in all which a S. W. Moon makes high Water and the same is reported to be on the West side of America But it would be endless to accont for all those particularities which are consequences of this Hypothesis as why Lakes such as the Caspian Sea and Mediterranian-Seas such as the Black-Sea the Streights and Baltick have no sensible Tides For Lakes having no communication with the Ocean can neither encrease nor diminish their Water whereby to rise and fall and Seas that communicate by such narrow Inletts and are of so immense an extent cannot in a few hours time receive or empty Water enough to raise or sink their Surface any thing sensibly Lastly to demonstrate the excellency of this Doctrine the example of the Tides in the Port of Tunking in China which are so extraordinary and differing from all others wee have yet heard of may suffice In this Port there is but one Flood and Ebb in 24 hours and twice in each Month viz. when the Moon is near the Equinoctial there is no Tide at all but the Water is stagnant but with the Moons declination there begins a Tide which is greatest when she is in the Tropical Signs only with this difference that when the Moon is to the Northward of the Aequinoctial it flows when she is above the Earth and Ebbs when she is under so as to make high Water at Moons setting and low Water at Moons rising But on the contrary the Moon being to the Southward makes high water at rising and low water at setting it Ebbing all the time she is above the Horizon As may be seen more at large in the Philosophical Transaction Num. 162. The Cause of this odd Appearance is proposed by Mr. Newton to be from the concurrence of two Tides the one propagated in six hours out of the great South-Sea along the Coast of China the other out of the Indian-Sea from between the Islands in twelve hours along the Coast of Malacca and Cambodia The one of these Tides being produced in North Latitude is as has been said greater when the Moon being to the North of the Equator is above the Earth and less when she is under the Earth and contrarywise the other Tide that comes out of the Indian-Sea being raised in South Latitude is greater when the Moon declining to the South is above the Earth and less when she is under the Earth so that of these Tides alternately greater and lesser there comes alwaies successively two of the greater and two of the lesser together every day and the high-water falls alwais between the times of the arrival of the two greater Floods and the low-water between the arrival of the two lesser Floods And the Moon coming to the Equinoctial and the alternate Floods becoming equal this Tide ceases and the Water stagnates but when she has passed to the other side of the Equator those Floods which in the former order were the least now becoming the greatest that that before was the time of high water now becomes the low-water and the converse So that the whole appearence of these strange Tides is without any forcing naturally deduced from these principles and is a great argument of the certainty of the whole Theory If by reason of the difficulty of the Matter there be any thing herein not sufficiently explained or if there be any material thing observable in the Tides that I have omitted wherein your Majesty shall desire to be satisfied I doubt not but if your Majesty shall please to suffer me to be admited to the honour of your Royal Presence I may be able to give such an account thereof as may be to your Majesties full content