offering to our view some very remarkable pheno mena Soon as the ev'ning shades prevail, Whilst all the stars that round her burn, And spread the truth from pole to pole." As the orbit of the moon is constantly varying in its position, and the place of the node always changing, as her motion is even variable in every-part of her orbit, the solutions of the problems which relate to her, are not altogether so simple as those which concern the sun. The moon increases her longitude in the ecliptic every day about 13 deg. 10 min. by which means she crosses the meridian of any place about 50 min. later than she did the preceding day. Thus, if on any day at noon her place (longitude) be in the 12th deg. of Taurus, it will be 13 deg. 10 min. more, or 25 deg. 10 min. in Taurus on the succeeding noon. It is new-moon when the sun and moon have the same longitude, or are in or near the same point of the ecliptic. When they have opposite longitudes, or are in opposite points of the ecliptic, it is full-moon. To ascertain the moon's place with accuracy, we must recur to an ephemeris; but as even in most A A ephemerides the moon's place is only shewn at the beginning of each day, or XII o'clock at noon, it becomes necessary to supply, by a table, this deficiency, and assign thereby her place for any intermediate time. In the nautical ephemeris, published under the authority of the Board of Longitude, we have the moon's place for noon and midnight, with rules for accurately obtaining any intermediate time; but as this ephemeris may not always be at hand, we shall insert, from Mr. Martin's Treatise on the Globes, a table for finding the hourly motion of the moon. In order, however, to use this table, it will be necessary, first, to find the quantity of the moon's diurnal motion in the ecliptic for any given day; for the quantity of the moon's diurnal motion varies from about 11 deg. 46 min. the least, to 15 deg. 16 min. when greatest. The following tables are calculated from the least of 11 deg. 46 min. to the greatest of 15 deg. 16 min. every column increasing 10 minutes; upon the top of the column is the quantity of the diurnal motion, and on the side of the table are the 24 hours; by which means it will be easy to find what part of the diurnal motion of the moon answers to any given number of hours. Thus, suppose the diurnal motion to be 12° 32', look on the top column for the number nearest to it, which you will find to be 12° 36', in the sixth column; and under it, against 9 hours, you will find 4 deg. 43 min, which is her motion in the ecliptic in the space of 9 hours for that day. the diurnal motion for any day is The quantity of found by taking the difference between it and the preceding day. Thus, let the diurnal motion for the 11th of May, 1787, be required. TABLES FOR FINDING THE HOURLY MOTION OF THE MOON, AND THEREBY HER TRUE PLACE AT ANY TIME OF THE DAY. TABLE 1. HOURS. 11 46 11 56 12 6 12 16 12 26 12 36 12 46 12 5613 6 13 16 13 26 d. m. d. md. m. d. m. d. m. d. m. d. m. d. m. d md. m. d. m. HOURS. TABLE II. 13 30 13 40 13 50 14 6 14 16 14 26 14 36 14 4614 5615 615 16 d. md, md. m. d. m. d. m. d. m. d. m. d. m. d. m. d. m. d. m. 9 21 9.12 9 37 9 44 9 51 9 57 10 4 10 11 10 13 10 20 10 28 10 33 10 42 10 49 10 49 10 57 11 4 11 12 11 19 11 27 16 9 4 9 11 9 17 9 11 26 11 34 11 41 11 49 11 57 12 5 12 2 12 10 12 18 12 27 12 35 12 42 12 38 12 40 12 55 13 413 13 13 21 5 13 14 13 23 13 33 13 41 13 50 13 50 43 13 59 13 59 14 9 14 10 14 28 14 38 14 36 14 36 14 46 14 56 15 6 15 16 |