BULLIALD (Ismael)

, an eminent astronomer and mathematician, was born at Laon in the Isle of France in 1605. He travelled in his youth, for the sake of improvement, and gave very early prooss of his astronomical genius; and his riper years rendered him beloved and admired. Riccioli styled him, Astronomus prosimdæ indaginis. He first published his disser- | tation intitled, Philolaus, sive de vero Systemate Mundi; or his true system of the world, according to Philolaus, an ancient philosopher and astronomer. Afterward, in the year 1645, he set forth his Astronomia Philolaica, grounded upon the hypothesis of the earth's motion, and the elliptical orbit described by the planet's motion about a cone. To which he added tables intitled, Tabulæ Philolaicæ: a work which Riccioli says ought to be attentively read by all students of astronomy.—He considered the hypothesis, or approximation of bishop Ward, and found it not to agree with the planet Mars; and shewed in his defence of the Philolaic astronomy against the bishop, that from four observations made by Tycho on the planet Mars, that planet in the first and third quarters of the mean anomaly, was more forward than it ought to be according to Ward's hypothesis; but in the 2d and 4th quadrant of the same, the planet was not so far advanced as that hypothesis required. He therefore set about a correction of the bishop's hypothesis, and made it to answer more exactly to the orbits of the planets, which were most eccentric, and introduced what is called, by Street in his Caroline Tables, the Variation: for these tables were calculated from this correction of Bulliald's, and exceeded all in exactness that went before. This correction is, in the judgment of Dr. Gregory, a very happy one, if it be not set above its due place; and be accounted no more than a correction of an approximation to the true system: For by this means we are enabled to gather the coequate anomaly a priori and directly from the mean, and the observations are well enough answered at the same time; which, in Mercator's opinion, no one had effected before.—It is remarkable that the ellipsis which he has chosen for a planet's motion, is such a one as, if cut out of a cone, will have the axis of the cone passing through one of its foci, viz, that next the aphelion.

In 1657 was published his treatise De Lineis Spiralibus, Exerc. Geom. & Astron. Paris, 4to.—In 1682 came out at Paris, in folio, his large work intitled, Opus novum ad Arithmeticam Infinitorum: A work which is a diffuse amplification of Dr. Wallis's Arithmetic of Infinites, and which Wallis treats of particularly in the 80th chapter of his historical treatise of Algebra.—He wrote also two Admonitions to Astronomers. The sirst, concerning a new star in the neck of the Whale, appearing at some times, and disappearing at others. The 2d, concerning a nebulous star in the northern part of Andromeda's girdle, not discovered by any of the ancients. This star also appeared and disappeared by turns. And as these phenomena appeared new and surprizing, he strongly recommended the observing them to all that might be curious in astronomy.