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necessary to say any thing on this occasion: For the really practical question at present is, whether elementary works for the instruction of students in the Oriental languages, might not advantageously be composed in such a conventional character? By substituting this for the various alphabets now used, some trouble would certainly be saved to beginners, and much expense to the East India Company. The experience and acknowledged success of Dr Gilehrist in teaching Hindustani, by an analogous method, affords some confirmation to the theory of M. de Volney.
Art. VII. An Elementary Treatise or Astronomy. By Robert
Woodhouse, A.M. F.R.S. Fellow of Caius College, Cam
bridge. Vol. I. 1812. Vol. II. 1818. It is always an interesting speculation to trace the progess of
Science, from the first feeble efforts which mark its intancy, to the majestic and matured systems which have been strengthened by discovery, and established by time: And there is no one in which this progressive improvement is so well marked as in Astronomy. The progress has been so rapid and continued, that we can follow its steps as distinctly and satisfactorily as we can retrace the events of our own lives. The explanation of the phenomena of the Heavens, which was first suggested to the mind of Copernicus, and afterwards, in spite of the religious bigotry and superstition which characterized that age, promoted by his disciples, and extended by the rescarches of Galileo--the discovery by Kepler of the laws which govern the motions of the heavenly bodies—the general principle of universal gravitation upon which all those laws depend, established by Newton—the explanation of every inequality in the planetary motions, deduced by those who succeeded him from ihe immutability of the whole, and the proof of the same principle of gravitation—form the leading features which mark the advancement of Physical Astronoiny, from its first dawnings to the state of excellence in which we now behold it. Great as this excellence is, astonishing indeed for the limited capacity of man to have developed, it affords an explanation of a very minute portion only of the system of the universe. It brings us acquainted with the orbits of the earth and the planets round the sun, or rather round the centre of gravity of the solar system, and the motion of the secondary planets round the primary. But the sun himself must have a motion in fired space, by reason of the path which that centre of gravity describes about the centre of gravity of the whole universe. And yet, of
the sun's orbit in space, and the motion of the centre of gravity of our system, we are entirely ignorant. These investigations are reserved for the labours of future astronomers-if indeed we can look forward to the period when science shall perfect such dis, coveries, while we call to mind the long series of nges that elapsed before the motions of our own systeins were known and establish
It is the opinion however of La Place, a name justly celebrated in the annals of science, that we have already indications of the motions of the sun and stars. Speaking of these motions, he says, “ Les observations commencent à les faire appercevoir ; on a essayé de les expliquer par le seul déplacement du soleil, que parồit indiquer son nouvement de rot;ition. Plusieurs observations sont assez bien représentées, en supposant le système solaire, emporté vers la constellation d'Hercule. D'autres obscrvations semblent prouver que ces nouvemens apparens des étoiles, sont une combinaison de leur mouvemens réels avec celui du soleil. Les temps découvrira sur cet objct, des vérités eurieuses et importantes.'
The intimite extent of this field, where no bounds can be set to cur speculations, peculiarly shows the preeminence of Astronomy among all other pursuits of human wisdom. In metaphysics-- in literature-in the arts---ignorant as we are, we can assign limits, and supply, in imagination at least, all that may be wanting to perfection; but, in the works of Nature, beyond our power of scrutiny, we sec no end to our inquiries;- we pere ceive only the littleness of man, and the nothingness and vanity of all his boasted attainments.
Nevertheless, it is a great matter to have ascertained so perfectly the motions of the earth, and of the other planets and their satellites. In the last hundred years, discoveries have been made in this branch of science, which were deemed, by the older astronomers, above the reach of human reason and experience. As far as regards the system of which our globe forms a part, the theory is complete: All the motions of the planets round the sun-of the secondaries round their primaries--their mutual actions upon one another-the irregularities and inequalities produced by those actions--are most perfectly explained by that one mysterious power, their gravitation towards each other with forces that are directly as their masses, and inversely as the squares of their distances.
It is the proud boast of Great Britain to have been the birthplace of the man whose genius discovered this law; and, by it, accounted for the principal motions of our system. The foundations of Physical Astronomy were thus successfully laid. What Geometry could do for the superstructure, was also accomplished
by Newton: But it required more refined methods of calculation to complete the work; and the accomplishment of this was reserved for the introduction of the Integral Calculus, in the hands of his successors.
The speculations of Descartes first opened a field for the operations of the Calculos;-and from that time we may date the beginning of those discussions w! ich have agitated the mathematical world even to the present day. Geometry and Analysis were the standards round which the heroes of science rallied their forces; and so stoutly was the contest maintained by the keenness of the parties,-for even in Science the spirit of party has its sway,—that it was long doubtful which would be declared victorious. On the Continent, at length, and especially in France, the powerful operations of the Calculus began to make some impression ;-and the splendour of its achievements threatened a rapid destruction to its once formidable opponents. The effects of victory were soon apparent. In the hands of Clairaut, Euler, and D'Alembert, the improved analysis was making rapid strides towards the perfection of Physical Astronomy; and nothing was wanting but the assistance of La Grange and La Place to put a finishing hand to the whole.
In England, Geometry kept its ground for a much longer period, and even yet is niaking a faint stand at the very place from which it ought long since to have been dislodged. At that University which is considered as the nursery of mathematical learning in Great Britain, the works of Newton are still looked up to with all the reverence which is so justly due to them, but unhappily to the exclusion of that system so well calculated to extend the bounds of Science. The time, we trust, is not far distant, when the principles of Analysis will form a larger portion of the studies of that place ;-and we are sure nothing is so likely to hasten that period, as the publication of such mathematical works as that before us. At the other English University, the contest for preeminence between Geometry and Analysis has been little regarded. There, indeed, neither party have found supporters : Nay, it would be ridiculous to suppose that the merits of the case could be understood-far less advocated-at a place where the knowledge of a ponderous treatise on the Conic Sections is considered a great step in Sciencewhere the first few sections of the Principia are looked up to as heights unattainable to ordinary talent—and Dealtry's Fluxions esteemed the very summit of mathematical excellence.--Still less should we be warranted in hoping, that the doctrines of Analysis will ever there be received as the established faith. At present, we must be content with the infancy of Science;
they have made a beginning, at least ;-and it is some comfort to think, that even a small portion of mathematical knowledge, already shares the palm of academic honours with the dictates of Aristotle.
But it is time we should consider the work before us. It consists of two volumes, published at different times;—the first, containing Plane Astronomy;--the second, Physical. These subjects, and the mode of treating them, are so perfectly distinct, that we must consider these volumes as forming two separate works. We shall begin, accordingly, with the first, as being the most simple.
The natural divisions which Plane Astronomy takes, are, the Doctrine of the Sphere, including all Geographical Problems, -the Motions of the Sun and Moon, with their Eclipses,and the Phenomena exhibited in the Planetary Motions, as far as can be determined by observation.-Such, with some slight exceptions, is the order which Mr Woodhouse has adopted in the first volume of his Astronomy. In our observations on the different parts of this subject, and inquiries connected with them, we shall follow our author's arrangement.
After a familiar explanation of certain phenomena of the heavens, and a concise description of the most important instruments of the Observatory, Mr Woodhouse proceeds to give various methods for finding right ascensions and declinations of stars-their latitudes and longitudes, and also means of ascertaining the obliquity of the ecliptic, and the precession of the equinoxes. In all these, however, the observations are supposed to be made on the meridian; the Earth is considered as a mathematical point, at rest; and consequently the star, as truly seen in the direction in which the rays from it enter the eye of the spectator.
If such were the case, the labour to the practical astronomer would indeed be trifling.– With little else than to mark the hour br his time-piece, and the position of the star to which his instrument is directed, his observations would be complete as soon sis made, and his results would be free from the errors of calculation. But the Earth, it there be any truth in the Copernican System, is revolving in its orbit round the Sun, at the same time that it has a rotatory motion about its own axis,and even that axis has 2 oscillatory motion peculiar to itself. These and other causes must necessarily introduce error into his xrvations-and, to obviate their effects, requires all the ingepart of the astronomer. The methods which bave been adwe ar this purpose, are called Corrections; and, from their Etance, they form a very considerable part of this branca
of Astronomy.--Mr Woodhouse has very judiciously considered them in as early a period of the work, as was consistent with the explanations necessary to understand their use. A brief enumeration of these Corrections will not detain us long ;-and it is necessary to more fully understanding this part of the subject.
They are five in number, and are treated of in the following order. -1. Refraction. It is a well known law of Optics, that when a ray of light passes from a rarer into a denser medium, it is bent, or refracted, towards the denser. Hence the apparent place of a star will be changed: Being seen in the direction of a tangent to the curve formed by the refracted ray, it will appear elevated, but only in a vertical plane; and its declination being determined by its meridian altitude, will be affected by the whole refraction. To compensate for this error, a correction is necessary.
2. Parallax. That observations may be rendered the same for every part of the earth, they must be referred to some common point: this will naturally be the centre of the earth. The observer then, being supposed at this point, the object will appear depressed, in the direction of a vertical plane; and the quantity of this depression is measured by the difference of the angles, which the direction of the star makes with the zenith, at the surface and at the centre of the earth: The azimuth motion will not be affected ;-consequently the declination and right ascension will alone require correction.
3. Aberration. While a ray of light coming from a fixed star, passes through a telescope, the telescope having at the same time the motion of the earth in its orbit, the real path of the ray, relatively to the tube, is the diagonal of a parallelogram, the sides of which are proportional to the velocities of light, and of the earth. To view the star, therefore, in its proper direction, the tube must be inclined, so as to have the position of the diagonal of this parallelogram. Aberration, though necessarily very small, on account of the great velocity of light, is nevertheless one of the most important causes of error in observations: it affects both the longitude and latitude -the right ascension and the declination of a star. It is highly requisite, therefore, that corrections of these errors should be computed. And here, we cannot help remarking, how satisfactorily the phenomena of aberration prove the motion of the earth. However inconsistent with the simplicity of nature the Tychonic systern might be, there were yet no appearances that did not accord with, and we may almost say, strengthen and confirm, it. But the memorable discovery of Bradley, on