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about the rise acou
when she is in the signs Pisces and Aries, it may be asked why this remarkable rising is only observed in the time of harvest? The reason of this is not difficult to explain. In winter these signs rise about noon, and at that time, as the Sun is only about three signs from them, and the Moon is consequently in her first quarter, and rising when the Sun is near his meridian altitude, the phenomena are not perceived. In spring these signs rise with the Sun, as he is then in them; the Moon then being in conjunction, rises with the Sun, and of course is not visible. In summer these signs rise about midnight, and the Sun is again about three signs before them; the Moon is then in her third quarter, and rising so late, and giving but little light, the peculiarity in her rising is unobserved. But in autumn, these signs being opposite to the Sun, they of course rise when he sets, with the Moon in opposition, or about six signs distant from him; which being then at full, makes her peculiarity of rising very conspicuous at this time.
The circumstances above stated would take place yery regularly, if the orbit of the Moon coincided with the ecliptic; but as her orbit makes an angle with this circle, varying from 50 to 5° 18', and intersects it only at her rodes, her risings, when in the above two signs, will vary in different times; at some periods not differing more than 1 h. 40 m. in the space of seven days, while at other times this difference amounts to 3 h.; this depending on the position of the nodes with respect to these signs. These relative positions are constantly varying, as the nodes recede through the whole ecliptic in the space of 18 years and 228 days. This revolution will, therefore, cause the harvest moon to pass through the whole course of the most favourable as well as her least beneficial states in a period of about 19
It may also be remarked that the phenomena are by no means so favourable every year, as Mr. Ferguson makes them. The year 1820, however, is one of the favourable years, as the following statements will show: On September 15th, Moon Sets at 9b. 19 m. P. M. sionally seen in the evening of a warm day many weeks after it has retreated to its winter lurkingplace, or some weeks before it leaves it entirely in the spring. On these' occasions they are sure to meet with some provisions; for the same warmth that has roused them to activity, has brought out many of the insect tribe from their winter slumbers also.
16th, • - Do. - 10 - 19 • • . after which it will, of course, shine more and more favourably. Full Moon Sept. 22d, Moon rises 6 h. 9 m. P. M.
23d, - • • 6 21 · · ·
27th, · · · 8 7 · · · At this time twilight ends about 8 o'clock, and thus the light of the Moon will be serviceable in carrying in the harvest, from about the 15th to the 27th of September, almost a fortnight. By comparing the above numbers with the Moon's Risings and Settings, as given in the Almanacs for 1820, if these latter are rightly computed, they will be found to agree with both these risings and the settings as given below. .
It may be proper, in this place, to notice a peculiarity relative to the Moon, which evinces itself in the greatest degree in this year, 1820. The first differences,' as they are technically called, between two successive risings or settings, vary (cæteris paribusj more or less rapidly, as the declinations of the Moon do: and since the Moon passes from her greatest north to her greatest south declination, and back again in every lunar month, it follows that when the extreme declinations are a maximum with reference to the period of the nodes, or 18years, the variations in the first differences' are a maximum ; and vice versa. Now in 1811, when the Moon's node was in Virgo and Libra, her extreme declination north or south was a minimum, and could but little exceed 18° (in March 1811, it was 18° 11'); whereas 9 years after, that is, in May 1820, when the Moon's node will be in the first point of Aries, the
declination of the Moon is capable of being greater than in the former case by twice the inclination of the Moon's orbit, that is, it becomes augmented to 28° 44' north or south. Consequently, the variations in the first differences' are here the most rapid. They will gradually diminish from this limit; and in 1829, 1830, will be least rapid again: and so on.
The Moon's declination is equal to the obliquity of the eclipticthe inclination of the Moon's orbit.
The following times of the Moon's settings have
16th, . . . . . . . . . . 93
1 - 16 morping
2 . 27 . .
3 - 19 -
28th, · · · 5 · 19 · · · · - 9 Thus it appears, that though immediately after the new Moon, the first differences were about an hour and a half, yet in less than a fortnight they have diminished to less than a quarter of an hour. . ,
This period of the Moon's nodes also evidently occasions a great change in the possible altitude to which the Moon can rise when on the meridian. Thus in 1811, when the declination did not exceed 18° 11' N., the Moon could not rise higher when on the meridian (at London) than 18° 11' + 38° 28', or 56° 39'; whereas in 1820, when the declination may become 28° 44', the Moon's elevation on the meridian will be 28° 44' + 38° 28', or 670 12; exceeding the former by more than 10°. Her arcs of semiduration
above the horizon are, in these circumstances, proportionally augmented.
The circumstances above pointed out will also as evidently exercise a similar influence on the Moon's minimum altitude above the horizon, as on her maximum; for then the preceding numbers must be subtracted, and we shall have 38° 28°—28° 44', or 9° 44', for the Moon's least altitude above the horizon, when the greatest declination occurs at the times her nodes pass the points above specified.
The Naturalist's Diary
For SEPTEMBER 1820.
And gives to wintry storms the varied year,
To southern climes prepare their course to steer. • Of the summer birds of passage the different kinds of swallows are most numerous, and have attracted the most attention. They have so often been observed at sea, steering their course southward in autumn, and northward in spring, that no doubt can now be entertained as to the majority of them leaving us in the winter for the more genial warmth of the southern latitudes. There are, however, authentic accounts of some few being found in a torpid state, like bats, during the winter months. These individuals, probably by the lateness of their broods, or by some other accident, were necessarily detained till after the general migration, and were then unable, probably from want of food and strength, to undertake the journey. The same circumstance satisfactorily explains the transitory appearance of a few swallows so late in the year as November, and even December, when a warm sunny day has roused and brought out some of these torpid birds in search of a little food. The bat in the same manner, though it lies torpid most of the winter months, is occa
It has been observed too by naturalists, that great numbers of swallows have been sometimes seen early in the spring, have then totally disappeared for several days of cold weather, and have been on the wing again the first fine sunny day. As they cannot be supposed to have gone back again to warmer climates, and to have returned so soon, it is highly probable that these also have been for a few days in a state of torpor.
This disposition of the swallow to become torpid is evidently regulated by the temperature of the air, as has been satisfactorily proved by experiment. Swallows detained here, and not kept warm, have become torpid, whilst others, carefully preserved, have remained lively all the winter. . The torpid ones, gradually warmed, have likewise recovered their activity. That they have been endowed with this peculiarity for wise purposes cannot be doubted.
The sole food of the swallow we know to be insects; and as these only fly during warm weather, it is probable that, in a variable climate like this, these birds would occasionally suffer by being without food for a week or two together, particularly such as have come over rather sooner than the general flight, were it not for their capability of becoming torpid from the same cause that deprives them of their food.
The opinion, that swallows do not migrate, but spend their winter at the bottom of our ponds and lakes, though formerly pretty generally admitted, is too preposterous to be thought worth a moment's consideration by modern physiologists. Indeed, from