VIII.-Progress of European Science.

PRACTICAL ASTRONOMY.

Under this head may be comprehended all proceedings intended to bring us better acquainted with the phenomena of the heavenly bodies through the medium of observation and experiment :-the labours of astronomers in their observatories; the construction of new instruments; of new tables to facilitate calculations; of new maps of the heavens, &c. to which may be added pendulum experiments and the various geodetical operations on a grand scale, destined to the determination of the earth's figure. Of the latter branch of our subject, we have on a former occasion taken a cursory review, adverting to the survey now in progress in our own neighbourhood. In our last number also we anticipated the present notice by inserting an abstract of the contents of the new Nautical Almanac, which itself marks the progress of astronomical science, by the new wants that it is found necessary to supply to the practical astronomer to save the waste of his time in intricate calculations. We will now advert to the increased means set at work in the world for the pursuit of this noble and heart expanding-study, taking as our guide the annual reports of the president of the Astronomical Society: for in the present day, thanks to the systematic division of the sciences among their proper societies, information on each separate branch can be obtained at once without spending much time in searching through scattered notices in journals of general science.

Mr. SOUTH, in his address on the anniversary of February, 1830, congratulated the Society on the prosperous appearance of the astronomical horizon. He attributed with justice to the influence of the institution over which he presided, a part of the unusual activity prevalent, as well abroad as at home, in prosecuting observations, and in perfecting the theories and tables of celestial phenomena.

He noticed the establishment of no less than two new observatories endowed by the British Government: one at the Cape of Good Hope, under the Rev. Mr. FALLows; the other, the Paramatta Observatory, originally founded by Sir THOMAS BRISBANE in New South Wales, now converted into a permanent public institution. The East India Company had been equally active: they had remodelled their observatory at Madras, furnishing it with new instruments and appointing to the charge of them Mr. TAYLOR, an experienced astronomer from the Greenwich Observatory. An attempt had before been made to found an observatory at Bombay, which had failed through the bad management of the astronomer nominated there. At the anniversary of last February, the same illustrious president noticed the foundation of another observatory by the Company, in the Island of St. Helena, under the charge of Mr. JOHNSON and pari passu, the British Government had presented a 34 feet transit, by Troughton, and other valuable instruments, to the private observatory of M. DABADIE, on the Island of Mauritius, whither also a number of excellent instruments had been carried by Captain LLOYD, Surveyor General to the colony. Monsieur DABADIE's observations on the Comet of 1830 have brought this well-merited reward, not to himself alone, but generally to the zealous exertions of this scientific little island, which can boast of more than its due proportion of naturalists and literary men. Astronomy is well adapted to be the study of an insulated quiet seat of contemplation like this isle, or St. Helena, and some questions of great practical importance, such as that of the refraction on the oceanic horizon, might here be more successfully investigated than any where else.

Captain KING, R. N. also is mentioned as proceeding to New South Wales, provided with superior instruments for his own use.

Here is a goodly list of the astronomical emissaries from our own island, and yet it is doubtless full of omissions: for the amateurs must be more numerous in this than in any other science. Nothing of course was yet known in England of the appointment of Captain HERBERT as astronomer to the KING of Oude. From the magnificence conspicuous in all oriental undertakings, we may safely prognosticate, that the Lucknow Observatory will become a richly endowed establishment, if the life of the founder be spared to complete it. We cannot pause to follow the list of illustrious observers enumerated in Great Britain itself, at Cambridge, Dublin, Greenwich, Kew, London, and Edinburgh: nor of those on the continent, where the activity of the new observatories of Brussels, Cadiz, Cracow, and Geneva, are stated to be already rivalling the older establishments of Paris, Berlin, Moscow, Florence, and Vienna. Now let us see what has been produced at these rival observatories, for that is the best way to judge of their relative and positive merits. The Greenwich Observatory has lately issued a catalogue of 720 stars: selected and reduced from the catalogue formerly published by the Astronomical Society. This fundamental catalogue has now reached a degree of accuracy unexampled in astronomical history, and bids fair to preserve the credit of " the British Catalogue" of the good old times of FLAMSTEAD.

The Paris Observatory seems to have been dormant for a long time. A new transit and a splendid equatorial by Gambey have once more set it in activity, and an excellent rule of the Institute has imposed upon the superintendent the necessity of never being more than a year behind hand in publishing the results of his labours. Professor BESSEL has been employed upon pendulum investigations, and has come to the mortifying conclusion, that the corrections employed by British experimentalists are by no means correct! Mr. FRANCIS BAILY also has demonstrated the existence of certain imperfections in the apparatus which point out the necessity of fresh inquiries before the standards of weights and measures, upon which such care has already been spent, can be considered as finally settled!

Professor ENCRE has entitled himself as much to the gratitude of astronomers in general, as to the medal so justly awarded him by the Astronomical Society, for the Berlin Ephemeris, which bears his name. While the Nautical Almanac has been gradually retrograding, and the Connoissance des tems stationary, the Berlin Almanac has suddenly stept in advance of both, and so full are its contents, and so excellent its arrangement, that, as Mr. SOUTH saуs, "with it an observatory scarcely wants a single book; without it, every one." The new Nautical Almanac will be one of the fruits for which we are indebted to ENCKE's example, and we hope it may prove, according to the President's promise, “ as superior to ENCKE's, as ENCKE's is now superior to it."

The Royal Academy at Berlin has carried into complete effect its plan for a minute survey of the heaven, and for the formation of a new set of celestial charts. Three portions of this useful and valuable undertaking are already published: viz, the 10th hour in AR by professor GōBEL of Coburg, the 14th hour by the Rev. T. J. HUSSEY of Chisleburst, and the 18th hour by Padre GIOVANNI INGHIRAMI of Florence, and M. CAPOCCI of Naples. The catalogues contain a list of all the stars (reduced to the year 1800) within 15o of the equator down to the 10th magnitude: and when complete, will be a most valuable acquisition to the practical astronomer. Of the labours of one member of our own Royal Observatory, we must take a fuller review: we allude to those of Mr. RICHARDSON on the constant of aberration.

H

In extracting for this purpose the words of Mr. SOUTH's address on presenting the author with the gold medal, we are in fact giving a most luminous and interesting review of the history of this subject, so closely connected with the demonstration of the Copernican system.

"Three hundred years have now elapsed since COPERNICUS proposed to the world that system which bears his name; and if we except the labours of TYCHO BRAHE, who, besides a catalogue of 800 stars, made attempts to determine the altitude of the pole-star at different seasons of the year, little was done by practical observation to support or refute the ideas of COPERNICUS till the time of GALILEO. Observations of the eclipses of Jupiter's satellites induced him to propose them as a means of determining differences of longitude, whilst his discovery of the phases of Venus removed a serious objection to the truth of the Copernican system, and which COPERNICUS himself predicted would be removed, though he had not the means of doing so himself. About the year 1665, HUYGENS, by his invention of the pendulum clock, gave to astronomical observations an accuracy hitherto unknown; and CASSINI, by means of the excellent glasses of CAMPANI, accumulated a vast mass of observations of the eclipses of Jupiter's satellites, and deduced from them tables whereby astronomers could predict their occurrence..

"Notwithstanding the powerful arguments advanced in its favour, the Copernican hypothesis was not generally embraced; for in the year 1669, nearly a century and a half subsequent to its promulgation by COPERNICUS, even the celebrated Hook, to use his own words, would not absolutely declare for it*. To settle the matter, therefore, this extraordinary man, feeling that the instruments of TYCHо, although magnificent beyond all others, were, from the nature of their construction, and from their being unprovided with telescopic sights, incompetent to detect minute alterations of sidereal positions, and knowing that the laws which governed refraction were so little understood as to render all observations in which that element was materially involved, liable to errors greater probably than the quantities he was in search of, invented the zenith sector. It was erected at Gresham College, and consisted of a telescope, 36 feet long, a divided arc, and a plumb-line. The star selected for observation, and with reference to which, indeed, his instrument was entirely constructed, was one which passed within two or three minutes of the zenith of Gresham College; it was visible in the day-time throughout the year, and was ʼn Draconis : by observing its zenith distance when the earth was in opposite points of her orbit, he found (as he erroneously concluded) a sensible parallax, amounting to about 20 seconds, and, consequently, determined that the Copernican system was the true onet.

"In the mean time, the eclipses of Jupiter's satellites, thanks to the facilities of predicting them, afforded by CASSINI's tables, had been assiduously observed; and in the year 1675, the discordances found between the predicted and the observed eclipses enabled the celebrated ROEMER to demonstrate that light was not instantaneously propagated, and that the discordances between the tables and the observations might be considered as the measure of its velocity.

"The year of ROEMER's discovery was further marked by another epoch in astronomical history, namely, the foundation of the Royal Observatory. FLAMSTEAD,

* An attempt to prove the motion of the earth from observations made dy ROBERT HOOKE, F. R. S. pp. 5 and 7.

Idem, pp. 10 and 11.

+ Idem, p. 25.

with his mural quadrant, detected a change of place in the pole-star, amounting to 35, 40, or 45 seconds, attributed it to parallax, and regarded it as confirmatory of Hook's discovery. Indeed, the observations of Hook, as well as of those who preceded him, although nominally in search of parallax, had for their object little else than the confirmation or verification of the Copernican system; and this arrived at, there seems to have been but little disposition to repeat them.

"Hence it was that the brilliant discoveries of NEWTON having placed the accuracy of the Copernican system beyond all possibility of doubt, the investigation of parallax was not resumed till the latter end of November, in the year 1725, at which time MOLYNEUX erected his 24-feet zenith sector, by GRAHAM, in his observatory at Kew*. 'On the 3rd of December, y Draconis was, for the first time, observed as it passed near the zenith, and its situation carefully taken with the instrument; and again, on the 5th, 11th, and 12th, when, no material change in the star's place having been detected, further observations seemed needless, since it was a time of the year when no sensible alteration of parallax could soon be expected.' BBADLEY, however, being on a visit to his friend MOLYNEUX, was 'tempted by curiosity to repeat the observation on the 17th, and perceived the star pass a little more southerly than when it had been observed before:' suspecting that the apparent change of place might be owing to erroneous observation, it was observed again on the 20th, and he found the star still farther south than in the preceding observations. This sensible alteration surprised himself and MOLYNEUX, in as much as it was the contrary way from which it would have been, had it proceeded from an annual parallax of the star; but being incapable of accounting for it by want of exactness in the observations, and having no notion of any other cause from which such apparent motion could proceed, they suspected that some change in the materials of the instrument itself might have occasioned it. Under this apprehension, they remained some time, but being at length fully convinced, by repeated trials, of the great exactnesss of the instrument, and finding, by the gradual increase of the star's distance from the pole, that there must be some regular cause which produced it, they examined nicely at the time of each observation how much it was; and about the beginning of March,1726, the star was found to be 20" more southerly than at the time of the first observation. It now, indeed, seemed to have arrived at its utmost limit southward; for in several observations made about this time, no sensible difference could be detected in its situation. By the middle of April, it appeared to be returning towards the north, and about the beginning of June, it passed at the same distance from the zenith as it had done in December, when it was first observed. From the quick change in the star's declination about this time (it increasing a second in three days), they concluded that it would now proceed northward, as it before had gone southward of its present situation; and it happened as was conjectured; for it continued to move northward till September following, when it again became stationary, being then near 20' more northerly than in June, and no less than 39′′ more northerly than it had been in March. From September, it returned towards the south, till it arrived, in December, at the very same situation it had been at that time twelve months, allowing for the difference of declination 'on account of the precession of the equinox.'

“Such is a brief history of the Kew observations; commenced, indeed, for the determination of sensible parallax, but which, as subsequently in the hands of HER* Philosophical Transactions, vol. xxxv. p. 639,

SCHEL, led to a very different result. In reading it, we are at a loss whether most to admire the mode in which the observations were conducted, or the modest unassuming manner in which they are recorded: no possible source of error is allowed to pass without the most rigid examination-no theory suffered to embarrass the observers in their observations; the slightest anomaly became the subject of suspicion, till in presumed anomaly was found the most perfect regularity.

"That observations so conducted, leading to results so unexpected,could be abandoned till the law which governed them should be unfolded, was impossible. But BRADLEY rejected all inquiries into the cause till the effects were accurately determined; and feeling that the apparent motion was obtained by observations only of one year by one instrument—and by one star,-he erected at Wanstead, aided by his friend GRAHAM, on the 19th of August, 1727, his zenith sector of 124 feet focus, formed, indeed, upon the same general plan of MOLYNEUX's, but furnished with a divided arc of 64 degrees on each side of the zenith point, for the purpose of enabling him to ascertain, by direct observation, whether other stars than 7 Draconis would be similarly affected. The instrument's situation, when adjusted, 'might be securely depended upon to half a second,' and its telescope could be directed to not less than 12 stars, bright enough to be seen in the day-time,' throughout the year: the same changes were observed as had been previously detected with MOLYNEUX's instrument. Inflexible, however, in his resolution not to generalise till sufficient means were collected to lead him to a 'probably just conclusion,' the year of probation was suffered to be completed before the observations were examined and compared: then it was that he satisfied himself of the general laws of the phenomena, and then, and not till then, did he endeavour to find out their cause. Convinced that the apparent motion of the stars which he had observed was not owing to nutation-persuaded, that a change in the direction of the plumb-line with which the instrument was rectified was insufficient to have occasioned it—and having appealed unsuccessfully to refraction,—he perceived, 'that if light was propagated in time, the apparent place of a fixed object would not be the same when the eye is at rest, as when it is moving in any other 'direction than that of the line passing through the eye and the object; and that when the eye is moving in different directions, the apparent place of the object would be different.' He therefore announced his discovery in these words: That all the phenomena proceeded from the progressive motion of light and the earth's annual motion in its orbit,' or, as he afterwards called it, aberration of light.

"But he who determined its existence determined also its constant, and fixed it at 20"; giving us, therefore, the interval of time in which light travels from the sun to the earth, as eight minutes and seven seconds, differing from that deduced by ROEMER nearly three minutes of time, a circumstance not at all to the discredit of ROEMER, considering the imperfect knowledge of the theory of Jupiter's satellites at the time he made his important discovery.

"The observations, however, which led BRADLEY to the discovery of aberration, and to the determination of its constant, being as yet unpublished, have given rise to insinuations certainly ungenerous, and probably unjust. Impelled by more honourable feelings, our illustrious associate BESSEL, alluding to the observations of y Draconis made by BRADLEY when the sector was removed to Greenwich, says*, 'Cæterùm BRADELII observationes Wansteadianæ liberari possunt à sectoris mutabilitate, quum sæpiùs, eodem tempore, observatæ sint stellæ, in quibus aberrationi * Fundamenta Astronomiæ, p. 124.