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philosophers have converted to the purposes of utility and instruction. The Moon can only be eclipsed by the interposition of an opaque body, which intercepts from it the light of the Sun; and it is obvious that this opaque body is the earth, because the eclipses of the Moon never happen, except when the Moon is in opposition, and consequently when the earth is interposed between her and the Sun. The globe of the earth projects behind it a conical shadow, the axis of which is the straight line that joins the centres of the earth and Sun, and which terminates at the point when the apparent diameters of these two bodies become equal. The diameters of these two bodies, seen from the centre of the Moon in opposition, are nearly in the proportion of 3 for the Sun and 11 for the earth. Therefore the conical shadow of the earth is at least thrice as long as the distance between the earth and Moon, and its breadth at the point where it is traversed by the Moon more than double the diameter of that' luminary. The Moon, therefore, would be eclipsed every time it is in opposition, if the plane of the orbit coincided with the ecliptic. But in consequence of the mutual inclination of these two planes, the Moon, when in opposition, is often elevated above the earth's shadow, or depressed below it, and never can pass through that shadow unless when it is near the nodes. If the whole of the Moon's disk plunges into the shadow, the eclipse is said to be total ; if only a part of the disk enter the shadow, the eclipse is said
to be parmioon's divided intese parts ass is
The Moon's diameter, as well as the Sun's, is supposed to be, divided into 12 equal parts, called digits ; and so many of these parts as are darkened by the earth's shadow, so many digits is the Moon said to be eclipsed. All that the Moon is eclipsed above 12 digits, shows how far the shadow of the earth is over the body of the Moon, on that edge to which she is nearest at the middle of the eclipse.
Eclipses of the Sun only take place during the conjunctions of the Sun and earth; they are occasioned by the Moon's body being interposed between the Sun and earth, or, in other words, by the earth's being plunged in the shadow of the Moon. The Moon, though much smaller than the Sun, is so much nearer to the earth, that its apparent di. ameter does not differ much from the diameter of that luminary; and, in consequence of the changes which take place in the apparent diameter of these bodies, it happens that, in some positions, the apparent diameter of the Moon is greater than that of the Sun. If we suppose the centres of the Sun and Moon in the same straight line with the eye of the spectator placed on the earth, he will see the Sun eclipsed. If the apparent diameter of the Moon happen to surpass that of the Sun, the eclipse will be total; but if the Moon's diameter be the smallest, the observer, if properly situated, will see a luminous ring, formed by that of the Sun's disk, which exceeds that of the Moon's, and the eclipse in this case is called annular. If the centre of the Moon is not in the same straight line which joins the observer and the centre of the Sun, the eclipse can only be partial, as the Moon can only conceal a part of the Sun's disk: on these accounts, there must necessarily be a great variety in the appearances of solar eclipses. We may add also to these causes of variety, the elevation of the Moon above the horizon, which is the cause of considerable changes in the diameter; for it is a fact, well and generally known, that the Moon's diameter appears larger when she is near the horizon than when she is elevated above it: and as the Moon's height above the horizon varies according to the longitude of the observer, it follows that the solar eclipses will not have the same appearance to observers situated in different longitudes on the earth. One observer may see an eclipse which does not happen to another in
a different situation, and yet the latter as well as the former shall be above the horizon in the same hemisphere; and in this respect the solar differ from the Junar eclipses, which are the same to all the inhabi. tants of the earth..
We often see, says La Place, the shadow of a cloud, transported by the winds, rapidly pass over hills and valleys, depriving those spectators which it reaches of the light of the Sun that others are enjoying ; this is the exact image of a total eclipse of the Sun. A profound night, which, under favourable circumstances, may last from four to five minutes, accompanies these eclipses; the sudden disappearance of the Sun, with the solemn darkness that succeeds, fills all animals with dread; the stars, which had been effaced by the light of the day, show themselves in full lustre, and the heaven resembles the most profound night: round the lunar disk, à crown of pale light has been perceived, which is thought to be the solar atmosphere, for its extent cannot accord with the Moon, as it has been ascertained, by eclipses of the Sun and stars, that the lunar atmosphere is nearly insensible.
The Moon does not entirely disappear in its eclipse, but is still enlightened by a very faint light that comes to it by the Sun's rays inflected through the terrestrial atmosphere; and but for the great absorption of these rays by our atmosphere, its brightness would be more vivid than when at the full Moon. We may sometimes distinguish, particularly about the time of new Moon, that part of the lunar disk which is not enlightened by the Sun: this feeble light is the effect of the light which the illuminated hemisphere of the earth reflects upon the Moon : what proves this is, that it is most sensible at the time of new Moon, when the greatest part of this hemisphere is directed to the Moon; for it is clear that, to a spectator in the Moon, the earth will present a succession of phases, similar to that which
the Moon presents to us, but accompanied by a much more intense light, from the greater extent of the terrestrial surface.
Mountains of a great height rise up from the sur. face of the Moon; their shadows, projected on the plains, form spots which vary with the position of the Sun: upon the edge of the enlightened disk we see these mountains forming an indented border, extending beyond the line of light by a quantity, which lead to conclusions respecting their real height above the surface. We recognize likewise, by the direction of the shadows, that the surface is broken by cavities, nearly resembling the basons of our seas. Lastly, the lunar surface seems to exhibit traces of volcanoes: several observers have occasionally seen upon the unenlightened part a vivid light, which they have attributed to a volcanic eruption, and hence the formation of several new lunar spots has been accounted for.
The Naturalist's Diary.
Crowned with a wreath of lilies, breathing cool
This month is, generally, accounted the hottest in the year. In consequence of the excessive heat, an evaporation takes place from the surface of the earth and waters, and large clouds are formed, which pour down their watery stores, and deluge the country with floods; frequently laying the full-grown corn. These summer storms are generally attended by thunder and lightning. During the intense heat of this month, we eagerly seek the luxury of cooling shades. Bathing, too, is both agreeable and healthful at this time :
The pool transparent to its pebbly bed,
Invites the throbbing, half reluctant, breast
And now, with sunward face, he floating lies. Animals are oppressed with universal languor, and either bend their way to pools of water, the coverts of the forest, or to any place that will shade them from the almost vertical Sun. In a hot summer's noon,
They, starting, snap, The flowers, which blossomed in the last month soon mature their seeds, and hasten to decay. A new race succeeds, which demands all the fervid rays of a solstitial Sun to bring it to perfection.
At the beginning of the month, the beech (fagus sylvatica), the wild carrot (daucus carrota), the calathian violet (gentiana pneumonanthe), betony, nightshade (circæa lutetiana), lavender (lavendula spica), and the wild angelica (angelica sylvestris), have their flowers full blown; and the flowers of the white lily (lilium candidum) begin to open : the thistle, sowthistle, hawkweed, blue bottle (centaurea cyanus), marygold, golden rod, camomile, and sunflower; the whole race of sedums and cotyledons; and the aquatic and marsh plants, as bulrush, water-lily, &c. flourish this month.
The different tribes of insects, which, for the most part, are hatched in the spring, are now in full vigour; but the plenitude of their enjoyment is limited indeed, for they die at the approach of winter.