| 152 accompanied with parhelia or mock suns. Clouds of a white and fleecy appearance were, at the time, floating in the atmosphere, but so thin, as not to entirely obscure the blue Sky.-The wind blew very gently from the west by north-west. The cold being intense, especially for the time of year, and small crystals of ice or snow were visible, floating in the air.
The following diagram represents these beautiful phenomena as they appeared about half past seven o'clock, A. M. The magnitudes of the circles given in the following description may not be exact, as I was destitute of the proper instruments for their accurate measurement.
1st. Let z be the zenith directly under which the observer is stationed, looking to the east. Let the outer circle represent the horizon, surrounded by a very bright prismatic circle not far from 45 degrees in diameter; the lower limb of which extended below the horizon nearly 4 1-2 degrees. Its breadth and colours [colors] were about the same as that of a common rainbow; nearly all the prismatic colours [colors] were discernible; the red being on the concave part of the circle next the sun.
On each side of the sun, at a and b towards the north and south, there were two mock suns of different colours [colors], very splendid and bright in their appearance.
2nd. The sun was encircled by another halos k n i m, much larger, than the former, and parallel to it, being nearly 90 degrees in diameter and its lower limb being sunk below the horizon about 27 degrees. It exhibited the same colours [colors] as the first, though not so bright.
3d. At the tops of these circles, at c and i, were two inverted arches whose common centre [center] seemed to lay in the zenith. The upper arch, f i h, was exceedingly brilliant and beautifully coloured [colored], and appeared to be about 54 degrees the diameter, and that of the lower one, d c e about 99 degrees. Another parhelion or mock sun, appeared in the middle of the lower arch, at c, where it coincided with the circle first described, but its colours [colors] and brightness were inferior to those of the collateral mock suns at a and b.
4th. There appeared a circle, m b s a n t r, much larger than any I have yet described, being about 144 degrees in diameter, and of a uniform whiteness. It was about 18 degrees above the horizon, and parallel to it passing through the true sun, s, and the collateral parhelia, a and b, and also through two other parhelia, t and r, something about 90 or 100 degrees from the sun, one towards the north the other towards the south. The parhelia, t and r, were of a whitish colour [color], and not very distinctly seen. The intersections m and n, of this circle with the circle k i m, were rendered more distinctly visible than other portions of the two circles.
These beautiful and curious phenomena, doubtless owe their origin to the refraction of the sun's rays through the minute, though differently shaped prismatic crystals of ice and snow, which float in the atmosphere.
Equilateral and quadrilateral prisms of ice and snow, are formed by the process of crystalization [crystallization]; the former prisma [prism] having angels of 60 degrees, the latter, angles of 90 degrees. Rays of light from the sun, passing through the former, would necessarily, according to the established laws of refraction, produce a coloured [colored] or prismatic halo of about 45 degrees in diameter; while rays passing though the latter, would, as may be geometrically demonstrated according to the known laws of Dioptrics, produce a colored halo of about 90 degs. in diameter.
Halos may be artificially produced, by interposing transparent crystals between the eye and a luminous body, the diameters of which will depend on the refractive power and shape of the substance composing the crystals.
O. Pratt, A M,
Professor of Mathematics in the University of the City of Nauvoo.
March 23, 1843.
Mount Ætna.-An eruption of Ætna commenced in the latter part of last year, and to the latest accounts still continued. The smoke and flame have been clearly discernable [discernible] at Palmero, distant by an air-line, at least 90 English miles from the mount, This is the first erruption [eruption] which has been visible at Palmero since 1802. The height of Ætna by Cacemtar, Sir J. Herschell, and Capt. Smyth, is fixed at 10,874 feet, English.
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