son, imbibes a considerable portion of the water upon which its lower stratum presses; and hence, in the night-time, becomes condensed and hazy. As the morning rises, however, and the sunbeams resume their vigour, the atmosphere once more rarefies, and re-acquires its transparency. If it rarefy equably, and homogeneously, every object beheld through it must necessarily be exhibited in its real proportion and figure: but it happens, occasionally, that in some parts of its texture, it seems to be more closely inter. woven than in others; and hence in its general expansion, veins, or striæ, like those often discovered in glass, make their appear. ance, of different densities and diameters. In this case, every stria, like every globule of rain, in consequence of the variation of its density from the common density of the atmosphere, becomes a refracting or a reflecting body; in other words, a prism, or a mirror, or both. If, then, a single globule of rain, properly disposed, be able to produce a phenomenon so marvellous as that of the rainbow, what phænomena may we not expect, what variation, inversion, contorsion, and grotesque and monstrous representation of images, beheld through a column of the atmosphere, intersected by so many aerial prisms of different densities, and mirrors of dif. ferent surfaces, in which the catheti may be innumerable, and for ever varying? We may hence, moreover, readily trace the cause of an occasional duplication of images in the atmosphere, of a parhelion, and paraselene, or double sun, and double moon, from the reflection of these luminaries in an opposite part of the heavens, when they are a little above the horizon; as also of the very curi. ous mirage remarked by M. Monge, in the hot and sandy desert between Alexandria and Cairo; in which, from an inverted image of the cerulean sky intermixed with the ground scenery, the neighbouring villages appeared to be surrounded with the most beautiful sheeting of water, and to exist, like islands, in its liquid expanse, tantalizing the eye by an unfaithful representation of what was earnestly desired.

The mirage has not been suffered to lie neglected by the poets. It is to the aërial phantoms exhibited by this meteor, that Milton alludes, in the following verses:

As when, to warn proud cities, war appears
Waged in the troubled sky, and armies rush

To battle in the clouds; before each van

Prick forth the airy knights, and couch their spears,
Till thickest legions close; with feats of arms

From either side of heaven the welkin burns.

[Good's Lucretius, vol. ii. p. 25.

SECTION II.

Fata Morgana, or Optical Appearances of Figures in the Sea and Air, in the Faro of Messina.

As when a shepherd of the Hebrid Isles
Placed far amid the melancholy main,
(Whether it be lone fancy him beguiles,
Or that aerial beings sometimes deign
To stand, embodied, to our senses plain)
Sees on the naked hill, or valley low,
The whilst in ocean Phoebus dips his wain,

A vast assembly moving to and fro;

Then all at once in air dissolves the wond'rous shew.

THOMSON.

Various philosophical writers and travellers, and among them ⚫ur English travellers Brydone and Swinburne, make mention of a very striking phenomenon which occasionally appears in the Straits of Messina, and is known by the name of Fata Morgana, or, as some render it, the castles of the Fairy Morgana. The accounts differ from each other, as well with respect to the appearances, as the concomitant circumstances which are supposed to be necessary for producing them. How far the effects themselves may be subject to variation; or to what extent the imagination of the narrators, who speak of the exhibition as calculated to produce astonishment, may be subject to irregularitity, would admit of discussion; but the general certainty of the events is matter of universal notoriety, and admits of no doubt. I have not had the good fortune to meet with any of the authors who treat on this subject expressly from their own knowledge and observation, till lately that the Dissertation of Minasi was lent me by the Right Honourable Sir Joseph Banks, Bart, &c. In this treatise the facts are related with much simplicity and precision, and the philosophical reasoning of the author is kept distinct from the narrative. I have therefore chosen to collect the present account from this author.

His first chapter contains a description of the phenomenon. "When the rising sun shines from that point whence its incident ray forms an angle of about forty-five degrees on the sea of Reggio, and the bright surface of the water in the bay is not disturbed either by the wind or the current, the spectator being placed on an eminence of the city, with his back to the sun and his face to the sea ;—on a sudden there appear in the water, as in a catoptric theatre, various multiplied objects; that is to say, numberless series of pilasters, arches, castles well delineated, regular columns, lofty towers, superb palaces, with balconies and windows, extended alleys of trees, delightful plains with herds and flocks, armies of meu on foot and horseback, and many other strange images, in their natural colours and proper actions, passing rapidly in succession along the surface of the sea, during the whole of the short period of time while the above-mentioned causes remain.

"But if, in addition to the circumstances before described, the atmosphere be highly impregnated with vapour, and dense exhalations, not previously dispersed by the action of the wind or waves, or rarefied by the sun, it then happens that in this vapour, as in a curtain extended along the channel to the height of about thirty palms, and nearly down to the sea, the observer will behold the scene of the same objects not only reflected from the surface of the sea, but likewise in the air, though not so distinct or well defined as the former objects from the sea.

"Lastly, if the air be slightly hazy and opake, and at the same time dewy and adapted to form the iris, then the above-mentioned objects will appear only at the surface of the sea, as in the first case, but all vividly coloured or fringed with red, green, blue, and other prismatic colours."

The author therefore distinguishes three sorts of Fata Morgana: that is to say, the first at the surface of the sea, which he calls the Marine Morgana; the second in the air, called the Aërial Morgana : and the third only at the surface of the sea, which he calls the Morgana fringed with prismatic colours.

In a note in this chapter P. Minasi enquires into the etymology of Morgana. After various remarks, he thinks the opinion of those who derive this word, which is so foreign to the Roman idiom, from μωροσ tristis and yavi lætitia afficio, is not far from the truth; considering the great exultation and joy this appearance

produces in all ranks of people, who on its first commencement run hastily to the sea, exclaiming Morgana, Morgana! He re marks that he has himself seen this appearance three times, and that he would rather behold it again than the most superb theatrical exhibition in the world.

In the second chapter the author describes the city of Reggio, and the neighbouring coast of Calabria: by which he shews that all the objects which are exhibited in the Fata Morgana are derived from objects on shore.

In his third chapter, consisting of physical and astronomical observations, he affirms that the sea in the straits of Messina has the appearance of a large inclined speculum; that in the alternate cur rent, or tide, which flows and returns in the straits for six hours each way, and is constantly attended by an opposite current along shore to the medium distance of about a mile and a half, there are many eddies and irregularities at the time of its change of direc. tion and that the Morgana usually appears at this period. Whence he enters into considerations of the relative situations of the sun and moon, which are necessary to afford high water at the proper time after sun-rise, as before described. It is high water, that is to say, the northern current ceases, at full and change, at nine o'clock. There is probably a small rise and fall, though the an notation to a large chart before me affirms that there is none.

In the fourth chapter and subsequent part of the work, the au thor collects the opinion and relations of various writers on this subject; namely, Angelucci, Kircher, Scotus, and others; and he afterwards proceeds to account for the effects, by the supposed in. clination of the surface of the sea, and its subdivision into different plains by the contrary eddies. The aerial effects are referred to considerations of saline and other effluvia suspended in the air; which I forbear to abridge, because it seems difficult to make any clear or productive statement either from the narrative or the reasoning.

What I seem to collect upon the whole from the several relations, brought into one point is as follows: 1. That by the situation of the Faro of Messina, the current from the south, at the expiration of which this phenomenon is most likely to appear, is so far impeded by the figure of the land, that a considerable por tion of the water returns along shore. 2. That it is probable the

same boasts may have a tendency to modify the lower portion of the air in a similar manner, during the southern breeze; or, in other words, that a sort of bason is formed by the land, in which the lower air is more disposed to become motionless and calm than elsewhere. 3. That the Morgana Marina presents inverted images below the real objects, which are multiplied laterally as well as vertically; and that there are repetitions of the same multiplied objects at more considerable vertical intervals. This I gather from the appearance of the dome and other objects in the plate. 4. That the Aerial Morgana is not inverted, but, as I am disposed to conjecture, is more elevated than the original objects. 5. That the fringes of prismatic colours are produced in falling vapours ; similar to many appearances which have been described by authors, but not accurately explained by the general principles of refraction through spheres of water. The ship is referred to by the author as an object surrounded by these fringes: whence it appears that the colours apply to the direct rays from objects, as well as to those of the Marine Morgana. 6. Various other objects in the drawing, at well as in the description, afford matter for question and conjecture, but none perhaps which it may be proper to enlarge upon, until the theory be better known. 7. It seems at all events more probable that these appearances are produced by a calm sea, and one or more strata of superincumbent air, differing in refractive, and consequently reflective power; than from any considerable change in the surface of the water, with the laws of which we are much better acquainted than with those of the atmosphere. 8. By attentive reflection upon the facts and reasonings in Mr. Huddart's paper, we may form a theory to account for the erect and inverted images: the polished surface of the sea may perhaps ac. count for the vertical repetition; but for the lateral multiplication we must have recourse to reflecting or refracting planes in the va. pour, which appear nearly as difficult to deduce or establish, as those which have been supposed on the water.

Swinburne gives the following account of this singular phenomenon, which we quote as affording a stronger proof of the correctness of the hypothesis advanced in the preceding section. Sometimes, but rarely, it (the Faro) exhibits a very curious phenomenon, vul.