The foregoing method of folving this Problem is nearly but not perfectly accurate. If very great exactnefs be required, the quantity of the moon's motion for the time after noon, and from thence her precife place in her orbit for the given time, fhould be found as directed in the 92d Problem. The moon's mean daily motion is about 13 degrees 10 minutes. EXAMPLES. On the 23d of January 1797, the moon's place was 14 deg. 47 min. of Sagittarius: proceeding agreeably to the above precept, it will appear that the rofe at London, on that day, a little after 4 o'clock in the morning; culminated at nearly half paft 8; and fet about half an hour after noon. Required the time of the moon's rifing, culminating, and setting at London on the following days: Jan. 4-Feb. 25-March 20-April 22-May 10 -June 18-July 14-Aug. 18-Sept. 1-Oct. 11 -Nov. 222-Dec. 19. PROBLEM XCVIII. To find the Amplitude, Azimuth, Altitude, &c. &c. of the Moon for any given Day, Hour, &c. having the Latitude of the Place given. Find the place of the moon in her orbit for the affigned day and hour; then her amplitude, &c. &c. may be found in the fame manner as already directed for the fun. See Problem 61, 62, and 15. PROBLEM PROBLEM XCIX. o illuftrate by the Globe the Phenomenon of the Harvest Moon. About the time of the autumnal equinox, when he moon is at or near the full, fhe rifes fooner fter fun fetting than fhe does in any other full noon week in the year: and the, moreover, rifes Imost at the fame time for feveral nights togeher. Thefe circumftances, with which farmers vere better acquainted than aftronomers till within hese few years, were gratefully afcribed to the goodness of God, conceiving that he had ordered t on purpofe to give them an immediate fupply of moon-light after fun-fet, for their greater conveniency in reaping and gathering in the fruits of the earth; accordingly, they diftinguish this full noon from all the others in the year, by calling it the barveft-moon. Mr. Ferguson has given a full account of the harveft-moon in his aftronomy; the fubftance of which is as follows, in a problem on the common celeftial globe : Make chalk-marks all round the globe, on the ecliptic, at 12 degrees 10 minutes from each other (beginning at Capricornus) a fpace equal to the moon's daily mean motion + from the fun; * The first perfon, it is faid, who attempted to account for this phenomenon was Mr. Johnfon, in his Queftiones Philofophicæ. The fecond edition of that little manual was published in 1735. + The moon's mean diurnal motion is 13 10', but as the fun moves nearly 1 in the ecliptic daily, the moon recedes from the fun only 12 1c' in the courfe of a day, or 24 hours. Y 2 then then elevate the North pole to the latitude of any place in Europe; fuppofe London, whofe latitude is 51 degrees North. This done, turn the ball of the globe round Weftward, and it will appear that different parts of the ecliptic make very different angles with the horizon, as thefe parts feverally rife in the Eaft: and confequently, in equal times, very unequal portions of the ecliptic will be elevated above the horizon. About Pifces and Aries, feven of thefe chalk-marks will rife in little more than two hours, as measured by the motion of the index on the horary circle: but about the oppofite figns, Virgo and Libra, the index will go over eight hours in the time that feven marks will rife. The intermediate figns will more or lefs partake of thefe differences as they are more or lefs remote from thofe above mentioned. Hence it is plain, that when the moon is in Pifces and Aries, the difference of her rifing will be little more than two hours in seven days; but in Virgo and Libra it will be eight hours in feven days; and this happens every month of the year, because the moon goes through all the figns of the ecliptic in a month, or rather in about 27 days. The moon is always oppofite to the fun when fhe is full, and the fun is never in Virgo and Libra but in our harvest months; and therefore the moon is never full in Pifces and Aries (which are the figns oppofite to Virgo and Libra) but in our harvest months. Of courfe, when the mocn is about her full in harveft, fhe rifes with lefs difference of time, or more immediately after funfet, than when he is full in any other month of the year. In our winter, the moon is in Pifces and Aries about the time of her first quarter, and rifes about noon; but her rifing is not then taken notice of, because the fun is above the horizon. In fpring, the moon is in Pifces and Aries about the time of her change; and then, as the gives no light, and rifes with the fun, her rifing cannot be perceived. In fummer, the moon is in Pifces and Aries about the time of her last quarter; and then, as fhe is on the decrease, and rifes not till midnight, her rifing generally paffes unobferved. But in harveft, the moon is full in Pifces and Aries (thefe figns, as we have before obferved, being oppofite to the fun in our autumnal months), and rifes foon after fun-fet for feveral evenings fucceffively; which makes her regular rifing very confpicuous at that time of the year. This would always be the cafe if the moon's path lay in the plane of the ecliptic; but as fhe moves in an orbit which makes an angle of about 54 degrees with the ecliptic, and croffes it in the two oppofite points called the nodes, her rifing, when in Pifces and Aries will fometimes not differ above an hour and forty minutes through the whole of feven days; and at other times, in the fame two figns, fhe will differ three hours and a half in the time of her rifing in a week, according to the different pofitions of the nodes with refpect to thefe figns; which pofitions, as. we have obferved in a former part of this work *, are conftantly changing, because the nodes go backward through the whole ecliptic in 18 years and 125 days. This revolution of the nodes will cause the harvest moons to go through a whole courfe of the most and leaft beneficial ftates, with refpect to the farmers, every nineteen years. A table exhibiting thefe variations, from the year 1751 to 1861, is inferted in the Cyclopædia, art. Moon. The year 1792 was one of the leaft beneficial, and the year 1802 was one of the most serviceable. OF THE SOLAR SYSTEM. A FAMILIAR EXPLANATION OF THE PLANETARY OR SOLAR SYSTEM. ΤΗ "H' expanded spheres, amazing to the fight, With all the curious meteors hovering there; The universe, throughout all space, is replenished with fyftems or worlds of different bodies. By a fyftem is meant a number of bodies which move around one centre. Such a fyftem is what we call the world; and the moving bodies of thefe fyftems we call planets or comets +, which, together with * The name planet is a Greek word fignifying “wanderer" the planets being erratic bodies continually changing their places. + From cometa, Latin, or from a Greek word denoting the hair: a hairy star. the |