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Creatures require Air of a determined Gravity to perform Respiration easily; for it is by its Weight that this Fluid intinuates itself into the Cavity of the Breast and Lungs : By a slow Circulation the Secretion of the Spirits is diminished; and, by the Want of the Force of Elasticity and Gravity, the Juices begin to ferment, change the Union of their Parts, break their Canals, and Diseases follow. Besides the above Causes, the Atmosphere may be put in Motion by the elastic Vapours forced from the Bowels of the Earth by subterraneous Heats, and condensed by whatever Causes in the Atmosphere. A Mixture of Effluvia of different Qualities in the Air may, by Rarefaātion, Fermentation, &c. produce Winds and other Effects like those resulting from the Combination of some chymical Liquors; and that such Things happen, we are assured from the Nature of Thunder, Lightning, and Meteors. From the Eruptions of Volcanoes and Earthquakes in distant Places, Winds may be propagated to remoter Countries. The divided or united Forces of the other Planets, and of the Comets, may variously disturb the Influence of the Sun and Moon, &c. We know that there happen violent Tempests in the upper Regions of the Air, when we below enjoy a Calm, and how many Ridges of Mountains there are on our Globe which interrupt and check the Propagation of the Winds, so that it is no Wonder that the Phaenomena we have ascribed to the Action of the Sun and Moon are not always constant and uniform, and that every Effect does not hereupon follow : which, were there no other Powers in Nature able to alter the Influence of, this might in a very regular and uniform Manner be expe&ted from it. That the rarefied Air ascends is sufficiently demonstrated by the Aerostatic Globe, or Air Balloon, lately invented ; this is a Globe made of Silk, or other light Stuff, made Air tight with Gum; which being filled with inflammable, or rarefied Air, will, when let loose, ascend until it comes to that Part of the Atmosphere that is nearly as light as the Air within it, where it will continue some Time. Some of these Globes have been made so large as to carry up Men with them, as have frequently been seen in Britain, France, and other Parts.
O F T I D E S.
WHE Tides, or the Flux and Reflux of the Sea, is that regular Motion of the Waters by which they rise and fall at certain equal Intervals of Time. . The Dočtrine of Tides remained in Obscurity, till the immortal Sir Isaac Newton explained it by his great Principle of Gravity and Attraction. For having demonstrated that there is a Principle in all
Bodies within the Solar System, by which they mutually attract each
...be 29 Days and an Half before they are upon the same Meridian again,
or in Conjunction, and about Half that Time, viz. I4 Days 18 Hours before they are upon opposite Meridians, or in Opposition. Now, as the Sun attracts the Earth, though much less than the Moon, being at so vast a Distance from it, yet when they are both upon the Meridian, either in Opposition or Conjunétion, that is, at Full and Change, their joint Attraction conspires to raise the Tides higher than when they act cross-ways. Hence the Tides are higher than ordinary twice every Month, and are called Spring Tides; but this does not happen till two or three Days after, when the Attractions of the Sun and Moon have been united some Time. But when the Sun and the Moon aét cross-ways, or are 90° asunder, the Tides are lessened in Proportion to the Difference of their Powers of Attraction, and produce what we call Neap Tides, which happen soon after the first and last Quarter of the Moon, when the Sun has lessen
ed the Attraction of the Moon for some Time. The Moon being the principal Cause of raising the Tides, they are always found to follow her, and consequently must always be shifting from West to East as the Moon does, so that it is High, Water at any Place when the Moon is upon the Meridian of that Place at Full or Change, it will be about 49 Minutes later on the following Day, 1 Hour 38 Minutes later on the second Day, falling back 49 Minutes every 24 Hours, until the Moon comes to the opposite Meridian ; and then it will be High Water again. These Tides regularly rise and fall twice in the 24 Hours, wherefore by knowing - the
the Time of the Moon's Southing at any Place, and the Time of High Water at Full or Change at that Place, we can find the Time of High Water on any other Day at the same Place, by allowing 49 Minutes later for every Day since the Full or Change, or 24 Minutes later for every Tide. - These Tides would be regular from West to East were the whole Earth covered with deep Water, but seeing their Course is obstructed by Land lying in their Way, surrounding-Islands, running up winding Rivers, and otherwise affected by Shoals, striking against Capes and Head-Lands, they are often forced to take long Circuits and various Directions to come to the Levels; that the Setting of the Tides and Times of High Water are different at different Places. . The Tides rising higher in Bays and Rivers than in the open Sea, is occasioned by its striking against the contračting Banks of Bays and Rivers, accumulate the Water, and cause it to rise higher than in the open Seas. The Tides are higher than ordinary twice every Year, viz. about the Vernal and Autumnal Equinoxes, and the Neap Tides less, which are occasioned by the Sun's being nearer to the Earth at these Times than at any other Time of the Year, and consequently the Power of Attraction is stronger; for by drawing up the Water when the Sun. and Moon are upon the Meridian, to a greater Height than ordinary, the Water 90° distant from the Meridian, must subside in the same
Water at any Place; is contained in the following Particulars:
To find the Leap Year. Divide the given Year by 4, if nothing remains it is Leap Year, but if 1, 2, or 3 remains, they shew that is so many Years after BiHextile, or Leap Year, as the Remainder is : thus the Year 1796 divided by 4, gives 449, and the Remail:der is (o) shews it is Leap Year.
To find the Golden Number for any Year. RULE. Add one to the given Year, and divide the Sum by 19 the Remainder will be the Golden Number.
t Required the Golden Number of 1796. ,
By adding one to that Year, it gives 1797, this divided by 19, gives 94 for the Quotient, and the Remainder is 11, the Golden Number
Year, to 30, because the Solar Year is 11 Days longer than the LuIkar
nar Year, and as the Epačt increases, it shews the Moon's Age at the Beginning of the Year; it is here supposed, that at the End of 19 Years, the Sun and Moon make all the Variety of Situations they possibly can with one another, and thence begin, and go over the same again. The Golden Number at the Birth of Christ was 1, which is the Reason that one is added to the given Year, to find the Golden Number. RULE. Divide the given Year by 19, the Remainder multiply by 11, and the Produćt will be the Epact; if it does not exceed 29, but if it does, subtract 30 from it as often as you can, and the Remainder will be the Epact, for it never exceeds 29.
E X A M P L E.
1796, divided by 19, gives 94, and the Remainder 10, multiplied by 11, gives 110 ; this divided by 30, gives 3, and the Remainder is 20 ; which is the Epact for 1796.
To find the Moon's Age.
To the Epačt, add the Day of the Month, and the Epačt, or Number for the Month ; the Sum if it does not exceed 30 is her Age ; but if it does, subtrast 30 from it, as often as you can, and the Remainder is her Age.
Note. The Epačt or Number for each Month is found thus: Divide the Number of Days contained between the first of January, and the first Day of any Month, by 29 #, the Remainder will be the Number for that Month. -
Required the Number or Epačt for Sept. 1796? Ans. 7.5
The Number of Days contained between the first of January 1796, and first of Sept. are 244 Days, divided by 29 #, gives 8 for the Quotient, and 7 # for the Remainder, which is the Number sought, and so for any other Month.
E X A M P L E. Required the Moon's Age April 29th, 1796. Day of the Month 29 Epačt for the Year 2O Number for the Month 3 30).52(I 3O
Number for the Months are nearly as follows: -- Jan. Feb. Mar. Apr. May. June. July. Aug. Sep. Oét. Nov. Dec. In com. Years o 2 o 2 2 4 4 6 7 8 Io Io In Leap Years o - 2 I 3 3 5. 5. 7 8 9 10 - 11 * * * * - S 2 To
Tofind the Maon's Southing on any Day of her Age.
Since the Sun returns to the Meridian he has left in the Space of 24 Hours, and the Moon, in about 24 Hours 49 Minutes, therefore, if the Moon leaves the Meridian at the same Time that the Sun does, on any Day, the next Day she will come to the Meridian 49 Minutes after him, falling back, about 49 Minutes every Day; whence to find the Time of the Moon's Southing, or coming to the Meridian, on any Day, we have this easy Rule :
Multiply the Day of her Age by 49, and divide the Produćt by 60, the Quotient is the Hours, and the Remainder the Minutes Afternoon when she souths. Or, which is rather easier, and in many Respects sufficiently exact for the Mariner's Purpose; Multiply the Moon's Age by 4, and divide the Product by 5, the Quotient is the Hours, and the Remainder multiplied by 12, gives the Minutes Afternoon when she is upon the Meridian; but if this Time exceeds 12, subtract 12 Hours from it, and the Remainder is the Time of her Southing in the Morning.
N. B. From the Full Moon to the Change she comes to the Meridian, or souths in the Morning, but from the Change to the Full in the Afternoon.
E X A M P L E. Required the Moon's Southing April 29, 1796
The Epact is 26 or thus 32 Number for the Month is 3 4. Day of the Month 29 -- - 5)88 3o)52(I -3o Moon's Southing 17 36 - - - I 2 OO Moon's Age 22 49 5 36 198 88 *--r 6,0)107.8 Moon's Southing 17 58 Afternoon Subtract - 12 oo Moon's Southing 5 58 in the Morning
Hence it appears that the Moon comes to the South, at 58 Minutes after 5 in the Morning.