brain? At all events, science owes him no great obligations for his discovery. But there still remained a newly fledged mathematician, young Gauss, now professor in the University of Göttingen.

own.

Charles Frederic Gauss was born in Brunswick, April 23, 1777.When at school he displayed striking indications of talent, and in his disputation for the Doctor's degree, he showed his acuteness and ingenuity, in the criticisms which he made upon the former attempts to demonstrate the first principles of algebra, at the same time proposing a new and rigorous demonstration of his But in 1801, he gave a more brilliant display of his powers in his Disquisitiones Arithmeticæ; a work full of the most refined mathematical speculation. This was the stripling, now twenty four years of age, who had the hardihood to attempt a problem in which all others had failed. Let us hear his own account of this discovery. "In the month of September, 1801, while engaged upon a labor of a very different kind, some ideas occurred to me which promised to lead to a solution of this great problem, the accurate determination of the orbit of a heavenly body from a small number of observations, independent of hypothesis. Not unfrequently in like cases, for fear of having our attention diverted from the main object of pursuit, we allow trains of thought to be forgot ten, which if followed up, might lead to important results. Perhaps my own reflections would have shared the same fate, if they had not occurred at a time singularly fortunate for their preservation. For about this time the report was circulated of the discovery of a new planet, and soon the observations of Piazzi were published. Never before in the annals of astronomy, has there occurred a better occasion, scarcely can we conceive a better one, for showing the importance of this problem, than that which now presented itself,

when the last hope of rediscovering this planetary atom, after the lapse of a year among the countless stars of the firmament, depended upon an accurate determination of the orbit founded upon those few observations. Could I have ever found a more fortunate moment for testing the practical value of my ideas, than by applying them to the determination of the orbit of Ceres, which during the forty days of observation had described an arc of only four degrees, and now after the lapse of a year, was to be sought in a remote part of the heavens? The application of my new method was first made in October, 1801, and on the first clear succeeding night, the fugitive was seen in the very place indicated by my computations."

The planet was rediscovered by De Zach, on the 7th of December, 1801, about 120° from the place where it was last seen by Piazzi. Jan. 5, it was seen by Dr. Olbers of Bremen; Jan. 26, it was seen by Mechain at Paris; and Feb. 3, it was observed by the Astronomer Royal at Greenwich. Since that time it has been constantly followed at all the large observatories, and its orbit is as well known as that of any of the planets observed by the astronomers of Chaldea.

Let us dwell for a moment upon these facts, and see if they contain any thing very extraordinary. Might not the whole scene have been laid at Alexandria or Babylon? The discovery of Ceres, was a matter of chance. Lucky Piazzi! Might not the same accident have happened to Hipparchus, or the astronomers of the Celestial Empire? Is there any thing in all this history which indicates the boasted superiority of the nineteenth century? And was the discovery of Gauss of any higher order than that of Columbus, who succeeded in making an egg stand upright on its smaller end?

The interest attaching to the discovery of this little body is rather

increased than diminished by its diminutive size. For ages it had pursued its silent pathway in the heavens, when no human eye was sufficiently acute to discover its exist ence. From the summit of the temple of Belus, the astronomers of Chaldea almost realized the poetic conception of touching the stars with their heads, yet no planet Ceres ever gladdened their eyes. Hipparchus first counted the stars, yet he never dreamed of the existence of this planetary atom. Still the Greeks and Chaldeans had eyes as acute as our own. Not one in a thousand of the people of these United States ever saw Mercury, and still fewer have ever had any evidence from their own observations of its being a planet. Yet Mercury was well known to the ancients, and still retains the name given to it by the Greeks. Through one of the fairest skies of nature, the Greek with eagle eye, sounded the depths of the firmament. In those primitive times, no short-sighted mortal strove to remedy the defects of nature with concave eye-glass. Nature had cast their physical forms in her most perfect mould. Compared with civilized man in modern times, the Greeks were superior in strength, in fair proportions, in acuteness of sense. Yet Hipparchus only counted 1022 stars, and even that great body Uranus had shone upon all the ancient world of astronomers, unnoticed and unknown. For ages had Ceres strown the plains of Sicily with her richest gifts, yet hitherto no mortal eye had presumed to gaze on the countenance of the goddess. The discovery of Ceres required the previous discovery of the telescope. This discovery dates back only two hundred years, and a telescope of sufficient perfection to disclose minute objects is of still more recent or igin. The discovery of Ceres is then a proof of the advanced state of the age in which it was made, as it required the use of a superior telescope.

This discovery not merely requir ed good optical power in the telescope, but several auxiliaries for accurate measurement. Simply to see the planet, requires mere optical power in the instrument. Ceres might then have been discovered with a bare telescope tube, without graduated circle, micrometer or vernier. From an observation of a single evening, however, it could not be distinguished from myriads of stars of equal size. It is shown to be a planet only by its motion, and to detect this requires a second day's observation. Our unmounted tube might have disclosed the planet on a second evening, and a quick eye, aided by diagrams, might have detected motion without measurement. The same thing might have been done on a third, a fourth, a fifth evening, and so on as long as the body was in sight. We say this might have been done. It is not physically

impossible-but almost infinitely improbable, that such a series of observations should be made with an unmounted tube, however excellent the object-glass, for reasons some of which are sufficiently obvious, and others can be duly appreciated only by the practical astronomer. But even this does not secure to us a permanent member of the planetary system. Ceres was visible only forty days, when it disappeared in consequence of its proximity to the sun. It became visible again only after the lapse of many months, when it was to be sought for in a distant part of the heavens. Without accu rate observations, and a computation of the orbit, the planet is irrecoverably lost. By accurate observations, we mean something of which the bulk, even of educated men, entertain no adequate conception. The ancients had acute senses, but proved clumsy observers. The astronomer royal of Alexandria was mistaken fifteen minutes in the latitude of his observatory, and Pytheas concluded that Marseilles and Constantinople

presented. There was wanting a method for deducing with facility and the greatest accuracy, the orbit of a new celestial visitor from a small number of observations. To this honor did Gauss aspire. At almost the same breath, his method was invented and applied; and the united voice of Europe accorded to him the credit of complete success. The discovery therefore of the planet Ceres, and the determination of its orbit, required a rare combination of circumstances; perfection of instruments-perfection in the modes of observation-perfection in the mathematical theory. It deserves therefore to be quoted as one of the proudest triumphs of science.

Another subject in which some definite progress has recently been made, is the distance of the fixed stars. The ancients placed the stars at a great but unknown distance, and it is certain that they had no instruments capable of measuring it. But soon after the invention of the telescope, the idea seems to have been entertained that now we might hope to learn the distance of the stars. We compute the distance of an inaccessible object, after measuring its bearing from two points sufficiently remote from each other. We compute the distance of the sun or a planet from the earth, by observing its direction from the extremities of the earth's diameter. The same method would be applicable to the stars if they were not too remote. Experience however has shown that this base line is too short. No instruments ever yet invented by man are delicate enough to indicate that one point of the earth is nearer to, or further from the stars than another. Astronomers have therefore endeavored to find a parallax in some of the fixed stars, by taking the diameter of the earth's orbit as a base line. Viewed from the extremities of a base line of Vol. II.

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a hundred and ninety millions of miles in length, it might be supposed there would be a great difference in the direction of some of the stars. More than a century ago, Hooke attempted to deduce an annual parallax from the observations of Flamsteed. The variation amounted to 47" from one solstice to another. The observations were good, but the inequality proceeded principally from aberration, which was then unknown, and could not be explained by parallax. Horrebow found the sum of the parallaxes of Sirius and Lyra 65"; between Sirius and the Head of the Dragon 124", from which he cal culated their distances. In 1717, Cassini found a parallax of 6" for Sirius; but Halley showed that this inequality might be ascribed to refraction.

At the commencement of the present century, astronomers had generally settled down in the opinion of Copernicus, that the parallax of the fixed stars was insensible. The inequalities which had been noticed in their places had been mostly explained by the discovery of aberration and nutation, and the small differences which still remained were so mixed up with the unavoidable errors of observation, that no satisfactory result could be deduced from them. If a parallax was ever to be discovered, it was clear that it must be exceedingly small in amount. This discussion was again revived by Dr. Brinkley, of Dublin.

John Brinkley was born in England, and was educated at Cambridge University, where he gradu ated in 1788, with the rank of senior wrangler. Being appointed to a fellowship in Caius College, he devoted himself with unabated zeal to the pursuits of science. Upon leaving Cambridge, he went to the University of Dublin to fill the chair of astronomy, left vacant by the death of Usher. An observatory had recently been erected, and

partially furnished with instruments. Among the instruments ordered, was an entire circle of ten feet diameter, movable on a vertical axis, for measuring altitudes. This circle was begun, as ordered, with a diameter of ten feet; but was reduced by Ramsden to nine feet, and afterwards to eight feet, of which last size it was finished. Only one other astronomical circle so large as this has ever been made, namely, that which was finished for Cambridge a few years ago, but which is not capable of moving in azimuth like the Dublin circle. This is the instrument with which Dr. Brinkley's observations were chiefly made. In the year 1813, he announced the following parallaxes as the result of twelve months' observations: a Aquila 3.0; Arcturus 1.1; a Cygni 0.9; a Lyra 0.7. The next year he published new determinations, differing not greatly from the preceding. Some astronomers in reply to these observations, objected that a change of temperature might occasion a change of figure in the circle. To this Dr. Brinkley replied, that other stars in the vicinity gave no indications of parallax. Why should a change of figure in the circle affect only the observations of the four preceding stars? The observations made at Greenwich by Pond, with Troughton's mural circle, not having confirmed Dr. Brinkley's results, he undertook, in 1818, a careful examination of all the errors to which mural circles are liable. His memoir, contained in the Philosophical Transactions of 1818, furnishes new determinations of parallax, founded upon all the observations made at Dublin, from 1808 to 1818. The result is, a Aquila 2.5; a Cygni 0.8; a Lyræ 0.7; 7 Draconis 0".0. Still, the astronomer royal at Greenwich determined to have no parallax; whereupon Dr. Brinkley, in 1821, renews the discussion of the prob

lem, and concludes with the following numerical results: a Aquilæ 1.6; a Lyra 1".2; Arcturus 0.6; a Cygni 0.3. It is worthy of remark, that these results differ materially from those before announced. The next year appeared another memoir announcing new parallaxes. The star which throughout furnished the greatest parallax, is a Aquila, and in this last memoir, finding that his observations of this star gave too great a value for the constant of aberration, Brinkley admits that the parallax deduced from them must be considered doubtful. From a comparison of the obser vations at Greenwich and Dublin, Pond derived the conclusion, that movable circles are less to be depended upon than mural. Brinkley maintains the contrary, and in 1824, gives his final results for a Lyræ. In 1827, Dr. Brinkley received the appointment of Bishop of Cloyne, a chair formerly occupied by the celebrated Berkeley. Henceforth, the man whose whole preceding life had been devoted to the contemplation of the firmament, and to the solution of the sublimest questions of science, divorced himself entirely from these enchanting occupations, to give himself exclusively to the duties of his new charge. To escape all temptation, the ex-astronomer royal of Ireland, the ex-Andrews professor of astronomy in the University, did not so much as retain in his house the smallest telescope. The disclosure of a fact so incredible, we owe to the indiscretion of a friend, who happening with the Bishop one day of an eclipse, was disappointed at not being able to observe it otherwise than with his naked eyes, for want of instruments. So soon may frail man leave his first love.

Thus stood the question of parallax only ten years ago. After the controversy between Brinkley and Pond, astronomers had mostly abandoned the idea of detecting a