FACTUM

, the product of two quantities multiplied together. As, the factum of 3 and 4 is 12; and the factum of 2a and 5b is 10ab.

FACULÆ, in Astronomy, a name given by Scheiner, and others after him, to certain bright spots on the sun's disc, that appear more bright and lucid than the rest of his body.

Hevelius assures us that, on July 20, 1634, he observed a facula whose breadth was equal to a 3d part of the sun's diameter. He says too that the maculæ often change into Faculæ; but these seldom or never into maculæ. And some authors even contend that all the maculæ degenerate into Faculæ before they quite disappear. Many authors, after Kircher and Scheiner, have represented the sun's body full of bright, fiery spots, which they conceive to be a sort of volcanos in the body of the sun: but Huygens, and others of the latest and best observers, sinding that the best telescopes discover nothing of the matter, agree entirely to explode the phenomena of Faculæ. All the foundation he could see for the notion of Faculæ, he says, was, that in the darkish clouds which frequently surround the maculæ, there are sometimes seen little points or sparks | brighter than the rest. Their cause is attributed by these authors to the tremulous agitation of the vapours near our earth; the same as sometimes shews a little unevenness in the circumference of the sun's disc when viewed through a telescope. Strictly then, the Faculæ are not eructations of fire and flame, but refractions of the sun's rays in the rarer exhalations, which, being condensed near that shade, seem to exhibit a light greater than that of the sun.