the meridional longitude of the eclipse, and is either east or west, as the eclipse happens before or after noon at Greenwich. Next, bring this meridional longitude to the brass meridian of the terrestrial globe, and elevate the pole which is nearest the Sun equal to his declination, and fix the globe in this position; then, if Jupiter be eastward of the Sun, draw a line along that part of the globe which coincides with the eastern horizon, which will pass over all those places where the Sun is setting at that time; but if Jupiter be westward of the Sun, draw the line along the western horizon, and it will pass over all the places where the Sun is then rising. When Jupiter is eastward of the Sun, add the difference of his and the Sun's right ascensions to the meridional longitude; bring the degree answering to their sum to the meridian, elevate the pole nearest Jupiter equal to his declination, and fix the globe in that position; then, another line being described on the globe, along the eastern horizon, the space included between this and the line of the Sun's setting before drawn, will comprise all the places where the eclipse will be seen during the interval between the setting of the Sun and that of the planet. But if Jupiter be to the westward of the Sun, the difference of the right ascensions must be subtracted from the meridional longitude, instead of being added to it, and the degree answering to the remainder brought to the meridian, the pole elevated, and the globe fixed as before. Thus, if a line be drawn along the western edge of the horizon, the space included between this line and that of the Sun's rising before drawn, will comprise all the places where the eclipse will be seen between the rising of Jupiter and that of the Sun. The eclipse will evidently be seen the best at those places that are most distant from these boundary lines; all the other circumstances attending it being the same.

It may also be ascertained if the eclipse will be

visible, by computation, and without the use of the globe; and for this purpose find the time of the Sun's rising and setting, by means of a table of semidiurnal arcs, as before described, for the required latitude. Find also the time of Jupiter's rising and setting, from the time of his passing the meridian and his declination, both of which are given in the Ephemeris, and the same table of semi-diurnal arcs. The manner of doing this has likewise been already pointed out.

When the immersion or emersion of either the first or second satellite has been accurately observed, according to mean time, at the place of observation, the longitude from Greenwich is immediately found by taking the difference between the time of observation and that stated in the Ephemeris, as the time of the same eclipse happening at the first meridian; and this difference, converted into degrees, minutes, &c., will give the difference of longitude between the two places, which will be east or west, as the observed time of the eclipse was greater or less than that given in the Ephemeris.

To illustrate this, let it be supposed that an emersion of the first satellite was observed, at the Cape of Good Hope, to take place at 9 h. 46 m. 38 s. of mean time, the time in the Ephemeris being stated to be 8 h. 33m. 5 s. The difference of these times is 1h. 13 m. 33 s., which, being converted into degrees, is equal to 18° 23′ 15", which is the longitude of the Cape east of Greenwich; since the time at which the eclipse is supposed to have happened at the Cape is greater than that stated in the Ephemeris, as the time of its happening at the Royal Observatory.

The most certain way, however, of deducing the longitude from an observation of this kind, is not to compare the time of its happening with that stated in the Ephemeris, but with that of an actual observation of the same eclipse, made at some place at which the longitude is well known when such an

observation has been made; for such a comparison avoids the errors to which the computations are liable. But if no corresponding observation of the kind can be obtained, it is desirable to find, by the nearest observations to the given time that have been made, what corrections the calculations of the Ephemeris require; and then the application of these corrections to the calculation of the given eclipse in the Ephemeris, renders it almost equivalent to an actual observation.

It has already been observed, that the immersions of Jupiter's first and second satellites alone are visible from his conjunction with the Sun to his opposition with that luminary; and from this time to his conjunction again the emersions only can be seen. But within about fifteen days, both before and after the conjunction, both the planet and his satellites are lost in the Sun's light; and consequently the eclipses are altogether invisible. This accounts for their generally being omitted in Time's Telescope for one month in the year. The reason why both the immersion and emersion of Jupiter's first and second satellites are not visible in the same eclipse, as well as the reason of the particular periods during which each is visible, will be clearly explained by the following simple diagram:

Let S represent the place of the Sun, EE' the Earth's orbit, mPn the orbit of Jupiter, and P the

place of the planet at the time of one of these eclipses. Also, let ise represent the orbit of one of his satellites, being the point of immersion, and e that of emersion. Now it is evident from the Figure, that when the Earth is at E before the opposition, a spectator would see the commencement of the eclipse, or the immersion, at i; but not the emersion at e; because the body of the planet will be between him and the point where the satellite issues from the shadow of the planet. And this will evidently be the case, as the planet moves in its orbit from its opposition to its conjunction. And, again, if the Earth were situated at E', the observer would see the emersion at the point e, but not the immersion at i; and this would evidently continue to be the case till the planet attained its conjunction, after which the observer would again see the opposite side of the planet; and, consequently, the immersions would become visible, and the emersions, for the same cause, be hid from his view.

The Naturalist's Diary

For NOVEMBER 1820.

The beauties of summer have vanished away,
Like volatile phantoms displayed in a dream;
And Phoebus diffuses an impotent ray,
Scarce yielding a smile to enliven the day,
Or brighten the breast of the stream.
And soon shall the forest its vesture bewail,
And valleys and hills wear an aspect forlorn;
No treniulous music shall sigh with the gale,
No flower its lustre disclose in the dale,
Nor blossom embellish the thorn.

THE gloominess of the weather in this month is proverbial: a love of nature is the refuge. He who grapples with March, and has the smiling eyes upon him of June and August, need have no fear of November.' Dr. Johnson has devoted the 12th No. of his Idler' to this subject; and although we

are not disposed entirely to deny the influence of the weather on the mind, we think that his observations are calculated to do much good with the majority of persons.

'Our dispositions,' he says, 'too frequently change with the colour of the sky; and when we find ourselves cheerful and good-natured, we naturally pay óur acknowledgments to the powers of sunshine; or, if we sink into dulness and peevishness, look round the horizon for an excuse, and charge our discontent upon an easterly wind or a cloudy day.

"Surely nothing is more reproachful to a being endowed with reason, than to resign its powers to the influence of the air, and live in dependence on the weather and the wind for the only blessings which nature has put into our power, tranquillity and benevolence. To look up to the sky for the nutriment of our bodies, is the condition of nature; to call upon the sun for peace and gaiety, to deprecate the clouds lest sorrow should overwhelm us, is the cowardice of idleness and idolatry of folly.

Yet, even in this age of inquiry and knowledge, when superstition is driven away, and omens and prodigies have lost their terrors, we find this folly countenanced by frequent examples. Those that laugh at the portentous glare of a comet, and hear a crow with equal tranquillity from the right or left, will yet talk of times and situations proper for intellectual performances, will imagine the fancy exalted by vernal breezes, and the reason invigorated by a bright calm.

If men who have given up themselves to fanciful credulity would confine their conceits in their own minds, they might regulate their lives by the barometer, with inconvenience only to themselves; but to fill the world with accounts of intellects subject to ebb and flow, of one genius that awakened in the spring, and another that ripened in the autumn, of one mind expanded in the summer, and of another