stances of the eclipse must first be determined for the centre of the earth; and if the parallaxes of the Sun and planet were nothing, these circumstances would be the same both for the centre and any point whatever on the surface: the difference therefore arises from parallax. Hence the results obtained for the centre may be regarded as first approximations very near the truth, to which the small corrections must be made that are necessary for transferring them to the different points of observation.

For this simple case, the question is precisely the same as for any other eclipse, and the formulæ we have already given for that purpose, in our fourth volume, are immediately applicable for computing the time of the transit. However, as there will not be another of these phenomena for more than fifty years, few of our readers will have an opportunity of comparing the result of the calculation with that of the observation, and we shall not therefore enter into a further explanation of the process; but merely observe that its application to the transit that took place in June 1769, gave the parallax of the Sun =8′′-5721, which answers to his distance from the earth at the time of the transit. But to bring this to his mean distance from the earth, it must be multiplied by the inverse ratio of these distances, which increases it by 0"-1296; and consequently the sum is 8"-7017, the solar parallax corresponding to his mean distance. The horizontal parallax of Venus,. as determined by the same process, is 30"-1149.

According to the calculations of the most eminent astronomers, the following transits of Venus are all that will occur between the years 1631 and 2110, with the days on which they will take place, viz.

been the first phenomenon of this kind that was either predicted or observed, which was done by Mr. James Horrox, a young astronomer of great genius and attainments, at Hool near Liverpool.

Delambre has calculated all the transits of this planet that will take place between the years 900 and 3000; and states 35 as the utmost number that can happen in that period. He also says, that in order that the passage may take place, it is necessary that the geocentric latitude of the planet multiplied by the cosine of the true inclination of its orbit must be less than the half sum of the diameters of the Sun and Venus. The geocentric latitude depends upon the heliocentric latitude, which also depends upon the distance of Venus from her node. From these considerations, this astronomer finds the following expression for the limit of the passage, or the distance of the planet from the node, which gives a simple contact, viz.

D_(s+p'—p). (V—v)

v sin I. cos I'

where D denotes the distance from the node, s the half sum of the diameters, p' and p the parallaxes of Venus and the Sun, V and v the true radii vectores, I the true, and I' the apparent inclination of the orbit.

If the distance from the node be less than this value, the passage will take place; but if greater, there will not be any passage.

OCCULTATION of the STARS.

Nearly related to the preceding subject is that of the occultation of the fixed stars, which implies the obscuration of these heavenly bodies by the Moon or a planet. The only method of ascertaining whether an occultation will happen is that of calculating the place of the Moon at the ecliptic conjunction. The course of the Moon, however, affords limits to these occurrences, which enable astronomers to judge when

they will take place; for Cassini has remarked that all stars, whose latitudes do not exceed 6° 36′ either north or south, may suffer an occultation on some part of the earth; and if the latitudes are not more than 4° 32', the occultation may happen on any part of the earth. To determine when these eclipses will happen, therefore, compute the time of the mean conjunction, and the true latitude of the Moon at that epoch; and then if the difference of the latitudes of the Moon and the star exceed 1° 37', there cannot be any occultation; but if this difference be less than 51', there must be an eclipse of the star on some part of the earth: between these limits the occultation may or may not take place.

The occultations which we notice in the course of our labours are those only that are visible at the Royal Observatory, at Greenwich; but the times specified will answer very nearly for most parts of the kingdom. In very distant places a great difference will result from the change in the Moon's parallax, and even this difference may be so great as altogether to prevent the obscuration from taking place. When an occultation of a fixed star by the Moon is observed in a place of well known latitude and longitude, it may be applied to the correction of the lunar tables; but if the latitude of the place only be well known, the observation may be applied for determining the longitude. This method of determining the longitude, however, though very correct, requires an accuracy of calculation which renders its troublesome to those persons who are not much accustomed to astronomical computations.

It would, however, be of great service to geography and navigation if travellers and mariners would make observations of this kind as often and as carefully as possible, as by this means the longitude of various places would receive correction, and the requisite calculations might be subsequently made, either by themselves, or scientific men to whom the results of

their observations might be submitted. The limits of our plan, however, preclude ás from explaining, in this place, the particular rules and methods by which this is to be accomplished.

The Naturalist's Diary

For FEBRUARY 1818.

Unlovely parent of the changeful hour,
Chill FEBRUARY, on thy palsied steps
All winter rages, with his savage train!

The leaden-coloured day both moist and bleak;
The shifting wind that round the compass veers;
And frequent from thy dripping wings pour down-
Cold showers or slippery sleet.

IN. February, the weather in England is usually variable, but most inclined to frost and snow. The thermometer is often down below the freezing point, but is generally found at noon between 36° and 46°; towards the end of the month it sometimes rises to 50°, or even 52° or 54°. The severe weather generally breaks up with a sudden thaw, accompanied by wind and rain; torrents of water pour from the hills, and the snow is completely dissolved. Rivers swell and inundate the surrounding country, often carrying away bridges, cattle, mills, gates, &c., and causing great injury to the farmer. But so variable is the weather in this month, that frequently frost again usurps the year.'

In the course of this month all nature begins, as it were, to prepare for its revivification. God, as the Psalmist expresses it, renews the face of the earth ;” and animate and inanimate nature seem to vie with each other in opening the way to spring. About the 4th or 5th, the woodlark (alauda arborea), one of our earliest and sweetest songsters, renews his note; a week after, rooks begin to pair; the thrush sings; and the yellow-hammer is heard; to which last the

amiable author of the Birds of Scotland' has the fol

lowing tributary lines:

Even in a bird the simplest notes have charms
For me: I even love the YELLOW HAMMER'S song.
When earliest buds begin to bulge, his note,
Simple, reiterated oft is heard

On leafless briar, or half-grown hedgerow tree;
Nor is he silent until autumn's leaves

Fall fluttering round his head of golden hue,
Fair plumaged bird!

The chaffinch sings; the green wood-pecker (picus viridis) makes a loud noise; and the redbreast continues to warble. Turkey-cocks strut and gobble. Partridges (tetrao perdix) begin to pair; the house pigeon has young; field crickets open their holes ; missel thrushes couple; and wood owls hoot ;-gnats play about, and insects swarm under sunny hedges; frogs (rana temporaria) croak, and the stone curlew (otis ædicnemus) clamours. By the latter end of this month, the raven (corvus corax) has generally laid its eggs, and begun to sit.

On antient oak or elm, whose topmast boughs
Begin to fail, the RAVEN's twig-formed house
Is built; and, many a year, the self same tree
The aged solitary pair frequent.

But distant is their range; for oft at morn
They take their flight, and not till twilight grey
Their slow returning cry hoarse meets the ear.

GRAHAME.

Moles (talpa europaeus) commence their subterraneous operations.-(See T. T. for 1814, p. 49.)

Soon as the potent frost relents, the soil
Relaxed admits the labours of the mole;
The darkling miner upward turns his heaps
In circles round the field; that to the swain
Annoyance brings, who drives his delving plough
Direct. For busy labour now prepares
For seed-time; and the toiling oxen roll
Their vacant eyes athwart the stubborn ground,
And bow with awkward gestures as they turn,
Oppressed beneath the galling yoke. Meanwhile
The hills are vocal by the ploughman's voice,
Resounding, as he cheers their struggling steps;