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The moon's path may be represented on the globe in a very pleasing manner, by tying a silken line over the surface of the globe exactly on the ecliptic; then, finding by an ephemeris the place of the nodes for the given time, confine the silk at these two points, and at 90 degrees distance from them elevate the line about 5 deg. from the ecliptic, and depress it as much on the other, and it will then represent the lunar orbit for that day.

PROBLEM XLI. To find the moon's place in the ecliptic for any given hour of the day.

You should be provided with an ephemeris,* that will give the moon's latitude and place in the ecliptie: first, note her place in the ecliptic upon the globe, and then counting so many degrees amongst the parallels in the zodiac, either above or below the ecliptic, as her latitude is north or south upon the given day, and that will be the point which represents the true place of the moon for that time, to which apply the artificial sun, or a small patch.

Thus, on the 11th of May, 1787, she was at noon in 2 deg. 35 min. of Pisces, and her latitude was 4 deg. 18 min.; but, as her diurnal motion for that day is 12, 48 in nine hours, she will have passed over 4 deg. 47 min. which, added to her place at noon, gives 7 h. 22 min. for her place on the 11th of May, at nine at night.

* The Nautical Almanack is the best English ephemeris, White's Ephemeris is a very useful manual. EDIT.

PROBLEM XLII. To find the moon's declination for for any given day or hour.

The place in her orbit being found by Prob. xli, bring it to the brazen meridian; then the arc of the meridian contained between it and the equinoctial will be the declination sought.

PROBLEM XLIII. To find the moon's greatest and least meridian altitudes in any given latitude, that of London, for example.

It is evident, this can happen only when the ascending node of the moon is in the vernal equinox ; for then her greatest meridian altitude will be 5 deg. greater than that of the sun, and therefore about 67 deg.; also, her least meridian altitude will be 5 deg. less than that of the sun, and therefore only 10 deg.; there will therefore be 57 deg. difference in the meridian altitude of the moon; whereas that of the sun is about 47 deg.

N.B. When the same ascending node is in the autumnal equinox, then will her meridian altitude differ by only 37 deg.; but this phenomenon can separately happen but once in the revolution of a node, or once in the space of 19 years: and it will be a pleasant entertainment to place the silken line to cross the ecliptic in the equinoctial points alter nately; for then the reason will more evidently appear, why you observe the moon sometimes with

in 23 deg. of our zenith, and at other times not more than 10 deg. above the horizon, when she is full south.

PROBLEM XLIV. To illustrate, by the globe, the phenomena of the harvest moon.

About the time of the autumnal equinox, when the moon is at or near the full, she is observed to rise almost at the same time for several nights together and this phenomenon is called the harvest

moon.

This circumstance, with which farmers were better acquainted than astronomers, till within these few years, they gratefully ascribed to the goodness of God, not doubting that he had ordered it on purpose to give them an immediate supply of moonlight after sun-set, for their greater convenience in reaping the fruits of the earth.

In this instance of the harvest moon, as in many others discoverable by astronomy, the wisdom and beneficence of the Deity is conspicuous, who really so ordered the course of the moon, as to bestow more or less light on all parts of the earth, as their several circumstances and seasons render it more or less serviceable.*

About the equator, where there is no variety of seasons, moon-light is not necessary for gathering in the produce of the ground, and there the moon rises

* Ferguson's Astronomy.

about 50 minutes later every day or night than on the former. At considerable distances from the equator, where the weather and seasons are more uncertain, the autumnal full-moon rises at sun-set from the first to the third quarter. At the poles, where the sun is for half a year absent, the winter moons shine constantly without setting, from the first to the third quarter.

But this observation is still further confirmed, when we consider that this appearance is only peculiar with respect to the full-moon, from which only the farmer can derive any advantage; for, in every other month, as well as the three autumnal ones, the moon, for several days together, will vary the time of its rising very little; but then in the autumnal months this happens about the time when the moon is at the full: in the vernal months, about the time of new-moon; in the winter months, about the time of the first quarter; and in the summer months, about the time of the last quarter.

These phenomena depend upon the different angles made by the horizon, and different parts of the moon's orbit, and that the moon can be full but once or twice in a year, in those parts of her orbit which rise with the least angles.

The moon's motion is so nearly in the ecliptic, that we may consider her at present as moving in it.

The different parts of the ecliptic, on account of its obliquity to the earth's axis, make very dif

ferent angles with the horizon as they rise or set. Those parts, or signs, which rise with the smallest angles, set with the greatest, and vice versa. In equal times, whenever this angle is least, a greater portion of the ecliptic rises than when the angle is larger.

This may be seen by elevating the globe to any considerable latitude, and then turning it round its axis in the horizon.

When the moon, therefore, is in those signs which rise or set with the smallest angles, she will rise or set with the least difference of time; and with the greatest difference in those signs which rise or set with the greatest angles.

Thus, in the latitude of London, at the time of the vernal equinox, when the sun is setting in the western part of the horizon, the ecliptic then makes an angle of 62 degrees with the horizon; but when the sun is in the autumnal equinox, and setting in the same western part of the horizon, the ecliptic makes an angle but of 15 degrees with the horizon; all which is evident by a bare inspection of the globe only.

Again,, according to the greater or less inclination of the ecliptic to the horizon, so a greater or Jess degree of motion of the globe about its axis will be necessary to cause the same arc of the ecliptic to pass through the horizon; and consequently the time of its passage will be greater or less in the same proportion; but this will be best illustrated by an example.

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