PARHELION

, or Parhelium, denotes a mock sun, or meteor, appearing as a very bright light by the side of the sun; being formed by the reflection of his beams in a cloud properly situated.

Parhelia usually accompany the coronæ, or luminous circles, and are placed in the same circumference, and at the same height. Their colours resemble those of the rainbow; the red and yellow are on that side towards the sun, and the blue and violet on the other. Though coronæ are sometimes seen entire, without any Parhelia; and sometimes Parhelia without coronæ.

The apparent size of Parhelia is the same as that of the true sun; but they are not always round, nor always so bright as the sun; and when several appear, some are brighter than others. They are tinged externally with colours like the rainbow, and many of them have a long siery tail opposite to the sun, but paler towards the extremity. Some Parhelia have been observed with two tails and others with three. These tails mostly appear in a white horizontal circle, commonly passing through all the Parhelia, and would go through the centre of the sun if it were entire. Sometimes there are arcs of lesser circles, concentric to this, touching those coloured circles which surround the sun: these are also tinged with colours, and contain other Parhelia.

Parhelia are generally situated in the intersections of circles; but Cassini says, those which he saw in 1683, were on the outside of the coloured circle, though the tails were in the circle that was parallel to the horizon. M. Aepinus apprehends, that Parhelia with elliptical coronæ are more frequent in the northern regions, and those with circular ones in the southern. They have been visible for one, two, three, or four hours together; and it is said that in North America they continue several days, and are visible from sun-rise to sun-set. When the Parhelia disappear, it sometimes rains, or there falls snow in the form of oblong spiculæ. And Mariotte accounts for the appearance of Parhelia from an infinity of small particles of ice floating in the air, which multiply the image of the sun, either by refracting or breaking his rays, and thus making him appear where he is not; or by reflecting them, and serving as mirrors.

Most philosophers have written upon Parhelia; as Aristotle, Pliny, Scheiner, Gassendi, Des Cartes, Huygens, Hevelius, De la Hire, Cassini, Grey, Halley, Maraldi, Musschenbroek, &c. See Smith's Optics, book 1, chap. 11. Also Priestley's Hist. of Light &c, p. 613. And Musschenbroek's Introduction &c, vol. 2, p. 1038 quarto.

PARODICAL Degrees, in an equation, a term that has been sometimes used to denote the several regular terms in a quadratic, cubic, biquadratic, &c, equation, when the indices of the powers ascend or descend orderly in an arithmetical progression. Thus, is a cubic equation where no term is wanting, but having all its Parodic Degrees; the indices of the terms regularly descending thus, 3, 2, 1, 0.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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PARAMETER
PARAPET
PARDIES (Ignatius Gaston)
PARENT (Anthony)
PARGETING
* PARHELION
PART
PARTICLE
PASCAL (Blaise)
PATE
PAVILION