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Catholic Europe deserves the distinction of having founded the first astronomical observatory worthy of the name. was erected at Nuremberg in 1472.** ** At this observatory many new methods of observation were invented, so that the revival of practical astronomy may be dated from its foundation." More than a century and a half elapsed before the observatory of Leyden was erected in 1632, and that of Copenhagen in 1641. Shortly after this the observatory of Paris, celebrated by the labors of the Catholic Cassini, was founded in 1667, and contemporaneously with it (1673), Father Verbiest enriched the old Peking observatory in China, founded in 1279, with the latest European scientific equipment. The Greenwich observatory followed in 1675.

In the United States the same interest was manifested, the observatory of Georgetown College being founded in 1844, the fifth in the order of time, and only seven years after the first in the country had been erected.

The Earth.

That the earth is spherical in shape was held as early as the eighth century by Virgilius, commonly called "The Geometer," who was Bishop of Salzburg, and by birth an Irishman. This doctrine of the earth's sphericity received a powerful impulse from the discovery of America by Columbus in 1492, and the encouragement which the great navigator received from the reigning Pontiff showed with what favor his theory was regarded in Church circles.

Copernicus (1473-1543) held not only the spherical shape of the earth, but also its rotation upon its axis, and although the only argument he could adduce in support of his theory was its overwhelming probability, his views were regarded with the greatest favor, and would soon have been adopted in all the schools, had they not received a serious check from the imprudence of Galileo.

The Abbe Picard, first president of the French Academy, was also the first to measure a meridian arc. This he did in

Encyclopedia Brittanica, 9th ed., title Observatory.

France in 1671, and thus obtained a correct knowledge of the true size of the earth. This latter result was so important that it at once gave us Newton's great theory of the universality of gravitation, for as a consequence of Picard's investigations, Newton was able to prove that the same force of gravity which holds bodies to the surface of the earth also controls the moon in her orbit with an intensity that diminishes as the square of the distance. The erroneous value of the size of the earth which Newton had used before, had long stood in the way of reconciling his theory with the moon's actual motion."

But the very first really experimental verification of the earth's rotation on its axis was given to the world in 1851 by Foucault, "that most ingenious of French physicists," by `means of a pendulum swung from the ceiling of the Pantheon in Paris. This experiment was received with the greatest enthusiasm, and has since been verified by thousands of experimenters.

Quite recently also, in 1896, but after eight years of patient labor, Father Carl Braun of Mariaschein, Bohemia, has given us a very reliable estimate of the earth's mass, that is, of its amount of matter, and consequently also of its density.8

The Sun.

After the telescope had been invented, the sun was the first celestial body that best lent itself to systematic study. It is immaterial to our purpose to decide whether Galileo or the Jesuit Scheiner was the first to discover the spots on the sun. It is certain, however, that Scheiner was the first eminent solar observer worthy of the name, since he was the first to devote his life to this work. He embodied the results of his investigations in a large volume, entitled "Rosa Ursina,"

A General Astronomy, C. A. Young, 1st ed., page 93. "Ibidem, p. 256.

"Ibidem, p. 95.

Die Gravitations-Constante, Die Masse und mittlere Dichte der Erde nach einer neuen experimentellen Bestimmung, by Carl Braun, S. J. Reviewed by J. H. Poynting in Annual Report of the Smithsonian Institution. 1902, p. 203.

printed in 1626-1630. In this work Scheiner establishes so many important facts that, according to the testimony of Winecke,' the labor of the re-discovery of several of them would have been spared to later astronomers if they had only consulted the "Rosa Ursina."

The spectroscope, with which the name of Fraunhofer will ever be associated, was another valuable instrument in the hands of astronomers. Father Secchi, of the Roman College (1849-1878), was quick to realize its value and to apply it to the sun and the stars. His work, "Le Soleil," appeared in 1870, and is the foundation upon which all modern theories respecting the sun are constructed. His explanation of the spots, faculæ, prominences and the corona, is substantially the same that is accepted to-day. He was ably seconded by his contemporary, Respighi, who had won such fame for himself especially in solar spectroscopy and by his catalogue of over twenty-five hundred stars and by his observations of comets and terrestrial magnetism, that the Italian government reinstated both him and Father Secchi in their respective observatories without requiring the oath of allegiance, which they could not take in conscience.

The Sun's Distance.

Probably the most important of all astronomical problems is the determination of the sun's distance from the earth, because upon this unit depends our knowledge of the dimensions of the individual planets, of the solar system and of the whole universe; in short, of the distance and size of all except the nearer celestial objects. Kepler's third law that the square of the time of any planet's revolution about the sun is proportional to the cube of its mean distance from it, enables us to pass from the earth's time of revolution (one year) and its mean distance, and the observed periodic time of any planet, to the latter's distance from the sun. And conversely, when a planet at times comes nearer to us than the sun, we can compute the sun's distance from the earth when we can find our

P. Christoph Scheiner, S. J., und seine Sonnenbeobachtungen, by John Schreiber, S. J., in Natur und Offenbarung, Vol. 48.

distance from the planet. Only two of the planets, Mars and Venus (and the asteroid Eros, only latterly discovered), can be used for this purpose. The sun's distance when found is then generally expressed in terms of its mean equatorial horizontal parallax, that is, the apparent angular magnitude of the earth's equatorial radius as seen from the sun at its mean distance from us.

It is to the credit of the Catholic Cassini, who lived in France in 1680, that he found the sun's parallax to be 9.5" and its distance from the earth 86,000,000 of miles, "giving the first reasonable approach to the true dimensions of the solar system." 10 Before his time Kepler had computed the sun's distance to be twelve or fifteen millions of miles, and Hipparchus had made it as low as four or five millions.

Venus, when in transit across the sun's face, may approach us almost within one-fourth of the sun's distance. This is why transits of Venus have been thought to offer the best possible solution of the great problem. In their great rarity, only two occurring in a century, astronomers have found an additional inducement to observe them carefully. Accordingly the astronomers of the eighteenth century strained every nerve to make successful observations of the transits of Venus which occurred in 1761 and 1769. Amongst others, Father Hell, director of the imperial observatory at Vienna, not only organized a corps of observers all over the world, but he went himself to Wardhus, in Lappland, in 1769, and thus occupied the most northerly station in Europe, so that his position was the most favorable for the purpose, the sun being, moreover, on the meridian at midnight at the middle of the transit. Owing to the storm then gathering about the Society of Jesus-it was suppressed four years later-and especially the accusations of the younger Littrow, one of his successors, Father Hell's observations were misunderstood and misinterpreted, so that he lay under a cloud of calumny for more than a century.

Encke, in 1824, made a thorough discussion of the transit observations, giving Father Hell's less weight than they de

10 Young, op. cit., p. 376.

served, and obtained the parallax 8.5776" (95,500,000 miles), a determination whose accuracy was "by no means commensurate with the length of the decimal," " since the very first place is now known to be wrong. In 1867 Newcomb went to Europe to re-examine the original observations. A close study of Father Hell's manuscript convinced him that the illustrious scientist had been seriously maligned, and he published a complete vindication of him.12 Taking Father Hell's observations into proper account, Newcomb obtained the parallax 8.79" (equivalent to 93 million miles), the latest and adopted value at present being 8.80". Father Hell had computed the parallax at 8.70", thus coinciding with Newcomb's in the first decimal, while Encke's prejudice against Hell's honesty had led him to vitiate this same first decimal by two units.

In the following century the British Government dispatched two distinct expeditions to observe transits of Venus, namely, to Kerguelen Island in 1874, and to Madagascar in 1882, giving the chief command on both occasions to Father Perry, of Stonyhurst College, England.

The Moon.

The moon, being our nearest celestial neighbor, was, naturally, the first of the heavenly bodies to come within the range of the telescope. Accordingly, Galileo gave the moon his special attention, and after establishing the true character of its surface, he even showed how the heights of the lunar mountains may be measured from their shadows.

The first map of the moon was published in 1645 in Spain by Langrenus, the King's cosmographer; the second in 1647 by the Protestant Hevelius, who rejected the nomenclature of lunar objects devised by Langrenus; and the third in 1651 by the Jesuit Riccioli, who restored and improved the original nomenclature so well that it has remained in use ever since.13

"Young, Elements of Astronomy, 1892, No. 511.

Monthly Notices of the Royal Astronomical Society of Great Britain, May, 1883, Vol. 43, p. 371, and also in the Astronomical Papers of the American Ephemeris, Vol. II, p. 301, et seq., and latterly in popular form in his Side Lights on Astronomy, Chapter XV.

History of Physical Astronomy, Robt. Grant, p. 229.

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