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are marked at the top of the other columns; and hence, when the Sun's declination and the latitude of the place is known, the semi-duration of the Sun above the horizon, corresponding to these given quantities, is found in the column answering to the latitude, and in the line with the declination, and is expressed in hours and minutes. This expresses the time of his setting, or that which elapses between his passing the meridian and the moment of his sinking beneath the western horizon; and, consequently, if this be taken from 12 hours, it will give the time of his rising on the same day. The declination which is to be used is that answering to noon of the given day. As an example, Let it be required to find at what time the Sun will rise and set on the 15th of April, 1820, in latitude 50°, the place being situated on the first meridian. The declination of the Sun answering to the time of his passing the meridian on that day, taken to the nearest minute, is 9° 50' north; then looking in the first column for go, in the same line, and the column answering to the given latitude is 6 h. 47 m. for the corresponding i time. But as there is 5 m. difference between the time answering to go and 10° of declination, fths of this must be added for the 50 m., which is 4m. 10 s.; and, consequently, 6 h. 51 m. 10 s. will be the time of the Sun's setting on that day. Hence we also have 12h.
- 6 h. 51 m. 10 s. = 5b. 8m. 50 s., or 8 minutes and 50 seconds past 5 in the morning, for the time of his rising.
Now it is evident, from the nature of these quantities, that double the time of his setting will be the length of his duration above the horizon, or the length of the day; and double the time of his rising will be the length of the night: in the present case the former is 13 h. 42 m. 20 s., and that of the latter 10 h. 17 m.
Again, Let it be required to find the time of the Sun's rising and setting at York, supposing it to be
in latitude 53° 58', on the 3d of August, 1820. In this case, neglecting the very slight variation in the Sun's declination between noon at the Royal Observatory and at York, the declination for that day will be 17° 30' north; and with 17°, and latitude 53, we have, in the table of semi-diurnal arcs, 7 h.40 m., to which 3 m. must be added for the 30' of declination, and 4 m. for the 58' of latitude; and hence the time required is 7 h. 50 m., which, taken from 12 h., gives 4 h. 10 m. for the time of his rising. These being doubled, also give 15 h. 40' for the length of the day, and 8 h. 20 m. for that of the night.
If it were required to find the time of the Sun's rising and setting at Tobolsk, in Asiatic Russia, on the 1st of October, 1820, we should have the latitude of the place, taking the nearest minute, which is always sufficiently accurate in cases of this kind, 58° 12' north, and the longitude 68° 6' east. Now the declination of the Sun, when he passes the first meridian of this country on the given day, is 3° 15' south; and the change in the preceding 24 hours is 23' 21"; and therefore for the 41 hours, answering to the difference of longitude, 4 must be subtracted, since the longitude is east, and the declination increasing, which makes the declination of the Sun, when that luminary passes the meridian of Tobolsk, equal to 3° 10' south. Hence, by the table at page 43 of the Ephemeris, we have 5 h. 45 m., corresponding to 3o of declination and 58° of latitude; to which 1' 13" must be added for the 10%' of declination, and 12 subtracted for the additional minutes of the latitude; and therefore the true time of the Sun's setting at Tobolsk, on the day proposed, will be 46 m. 1s. after 5; and the time of his rising 13 m. 59 s. after 6.
Here it may be observed, that when the Sun is approaching the zenith of the observer, that is, in these northern latitudes proceeding from the tropic of Capricorn to that of Cancer (or the contrary, on the south side of the equator), any change in his decli
nation augments the length of the day, but as he recedes from that point, such a change diminishes his duration above the horizon. On the other hand, an increase of latitude increases the longth of the day, when the observer and the Sup are both on the same side of the equator; and diminishes, it when they are on contrary sides of that cirole. The preceding examples illustrate these general precepts.
The Naturalist's Diary
For MAY 1820.
Decks the green hedge and dewy grass unshorn,
And now the Sun comes forth with level ray,
BAMPFYLDE. This month bright with sunshine, and fragrant with perfumes, covers the meadow with verdure and decks the gardens with all the mixtures of colorific radiance; a month from which the man of fancy draws new infusions of imagery, and the naturalist new scenes of observation. And yet there are some to whom these scenes are able to give no delight, and who hurry away from all the varieties of rural beauty, to lose their hours and divert their thoughts by a tavern dinner, the prattle or the politics of the day; or, to mix with a massof people as insensible as themselves. Such is, with some exceptions, a LONDON MAY often,
Chilled by rude gales, while yet reluctant May
What prudent cit dares yet the season' trust,
A’n't you quite tired? Pray, can we set you down? The latest species of the summer birds of passage arrive about the beginning of this month. Among these are the goatsucker, or fern-owl (caprimulgus Europæus), the spotted fly-catcher (muscicapa grisola), and the sedge-bird (motacilla salicaria). In this and the following month, tho dotterel is in season.
See our last volume, p. 133. - The charming minstrels of nature, who pour forth
such a concord of sweet sounds in this month, are well pourtrayed in 'Kleist's Vernal Season', as translated by Mr. Lloyd'. Although the scenery of this spring is sketched from the north of Germany, it may with little variation pass for that usually observed in Great Britain at this season.
In chorus full, ye feathered warblers, join
Pour from the alder top their varied lay.
The painted goldfinches delight to sport,
The silent vale and listening grove they fill. The insect tribes continue to add to their numbers; among these may be named several kinds of moths and butterflies (papilio atalanta, cardamines, egeria, lathonia, &c.)
To the BUTTERFLY.
-Yet wert tbou once a worm, a thing that crept
To burst a seraph in the blaze of day! Other insects now observed, are field crickets (gryllus campestris), the chaffer or may-bug (scarabæus melolontha), and the forest-fly (hippobosca equina), which so much annoys horses and cattle. The female wasp (vespa vulgaris) appears at thọ latter end of the month.