The Corona, or halo around the sun, moon, and stars, is easily illustrated by the zone formed by placing, during a frost, a lighted candle in a cloud of steam or vapour.
The Aurora Borealis is _arctic electricity_, and is beautifully imitated by the passage of an electric flash through an exhausted glass cylinder.
The rainbow is a combination of _natural prisms_ breaking the light into colours; and it may be seen in the cloud, or in the spray of the ocean, or in the beautiful cascades of Schaffhausen, Niagara, or Terni, or indeed in any foaming spray on which the _meridian_ sunbeams fall, or even in the dewy grass, lying, as it were, on the ground.
When the sun shines on a cloud, there is always a bow produced visible to all who are placed at the proper angle. The lunar rainbow is achromatic, or destitute of colour, because reflected light is not easily refracted into colour. In a brilliant sunset the floods of light around him often indicate the gradation of prismatic colouring.
CAST. In some waterfalls I have seen the Iris form a complete circle; as in the Velino at Terni, and in others, especially in Ionia and Italy. A perfect illusion is produced, for the bow seems to approach the spectator and then recede, as if Juno were sending her messenger on some special mission. There are many minds which would yield with delight to this conviction, and such probably was the illusion of Benvenuto Cellini—was it not? “This resplendent light is to be seen over my shadow till two o’clock in the afternoon, and it appears to the greatest advantage when the grass is moist with dew. It is likewise visible in the evening at sunset. This phenomenon I took notice of when I was at Paris, because the air is exceedingly clear in that climate, so that I could distinguish it there much plainer than in Italy, where the moists are much more frequent, &c.” A consciousness of superior talent, and probably the homage which was paid him even by the members of the holy conclave, were the springs of this flattering vision.
IDA. The beauty of these must light up even the fancy of a child, yet a holier feeling will ever inspire a Christian philosopher, when the bow is seen in the cloud, for it was the sign of the covenant. There is, indeed, something in the glories of the firmament which never fails to elevate my own thoughts, and I can readily sympathise with the Spanish religionists of the fifteenth century, and with the North Americans, who gaze upon the beautiful constellation of the “Southern Cross,” insulated as it is from all other stars in its own dark space; in solemn belief that it is the great symbolical banner held out by the Deity in approval of their faith.