When thou wakest at the morn.
SPECTRAL ILLUSIONS.
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BY THOMAS MILNER, M. A.
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A series of curious and interesting phenomena, involving the apparent elevation and approach of distant objects, the production of aerial images of terrestrial forms, of double images, their inversion, and distortion into an endless variety of grotesque shapes, together with the deceptive aspect given to the desert-landscape, are comprehended in the class of optical illusions. Different varieties of this singular visual effect constitute the mirage of the French, the fata morgana of the Italians, the looming of our seamen, and the glamur of the Highlanders. It is not peculiar to any particular country, though more common in some than others, and most frequently observed near the margin of lakes and rivers, by the sea-shore, in mountain districts and on level plains. These phantoms are perfectly explicable upon optical principles, and though influenced by local combinations, they are mainly referable to one common cause, the refractive and reflective properties of the atmosphere, and inequalities of refraction arising from the intermixture of strata of air of different temperatures and densities. But such appearances in former times were really converted by the imagination of the vulgar into supernatural realities; and hence many of the goblin stories with which the world has been rife, not yet banished from the discipline to which childhood is subject,—
“As when a shepherd of the Hebrid Isles
Placed far amid the melancholy main,
(Whether it be lone fancy him beguiles,