would furnish themselves with one of each description; so that the one globe would prove a mutual assistance to the other. *

That the opinions I have now expressed on this subject are not altogether singular, will appear from the following extract from Sir J. Herschel's "Astronomy," p. 162. "Of course we do not here speak of those uncouth figures, and outlines of men and monsters, which are usually scribbled over celestial globes and maps, in a rude and barbarous way, to enable us to talk of groups of stars or districts in the heavens, by names which, though absurd or puerile in their origin, it would be difficult to dislodge them. In so far as they have really any slight resemblance to the figures called up in imagination by a view of the more splendid constellations,' they have a certain convenience; but as they are otherwise entirely arbitrary, and correspond to no natural subdivisions or groupings of the stars, astronomers treat them lightly, or altogether disregard them, except for briefly naming particular stars, as a Leonis, B Scorpio, &c., by letters of the Greek alphabet attached to them." And again: "This disregard is neither supercilious nor causeless. The constellations seem to have been almost purposely named and delineated to cause as much confusion and inconvenience as possible. Innumerable snakes twine through long and contorted areas of the heavens, where no memory can follow them; bears, lions, and fishes, large and small, northern and southern, confuse all nomenclature, &c. A better system of constellations might have been a material help as an artificial memory."+

*The above remarks are abridged from two papers on this subject, which the author communicated twenty years ago to the London "Monthly Magazine" for October, 1818, and January, 1819, vol. 46, p. 201 and 500.

† Since the above was written, in April, 1938, I am happy to learn that the "British Association for the Advancement of Science" has had its attention directed to this subject. At the meeting at Newcastle in August, 1838, it was resolved, "That it is desirable that a revision of the nomenclature of the stars should be made, with a view to ascertain whether or not a more correct distribution of them among the present constellations, or such other constellations as it may be considered desirable to adopt, may be formed." At the meeting at Birmingham, August, 1839, the committee appointed to report on this subject stated, "That some progress has been made in reforming the nomenclature of the northern constellations; and that the stars in the southern have been commenced laying down on a planisphere, according to their observed actual magnitudes, for the purpose of grouping them in a more convenient and

CHAPTER IV.

ON THE DISTANCES OF THE STARS.

To measure the length and breadth of an extensive kingdom, and to compute its dimensions, or to determine the distances between two large islands or continents, was formerly reckoned an achievement of considerable magnitude; but to measure the whole earth, to compute its area, and to determine its exact figure and magnitude, were considered as the most astonishing enterprises ever attempted by man, and almost beyond the reach of the powers with which he is endowed. Confined to a small spot in the world in which he dwells, having no scale of measurement, in the first instance, but his own dimensions, or the length of a rod or chain formed from these dimensions, how can he measure spaces hundreds of times greater than the extent of his whole visible horizon? how can he compute the distances and dimensions of places which he has never visited, and some of which he never can visit, and embrace the whole amplitude of a world which has never been thoroughly explored? The height of his body is but a fathom, and the length of his chain but a score of fathoms; and such measures dwindle into mere points when compared with the dimensions of the earth. Hence it happened that many ages elapsed before the figure and dimensions of the world in which we dwell were nearly ascertained. The powers of the human mind, however, when called into action and properly exercised, are not only capable of such enterprises, but adequate to the performance of still more elevated achievements. When the mind of man is determined on the pursuit of knowledge, and bent upon improvement, difficulties, however great, only serve as incitements to action and perseverance, and to stimulate his energies to their highest pitch

advantageous manner." It is hoped, therefore, that we shall soon be presented with an arrangeinent and nomenclature of the starry groups accordant with the sublime conceptions and discoveries of modern astronomy, and which shall present, on our globes and planispheres, a more perspicuous and natural representation of the heavens.

of exertion. He multiplies small measures till he arrive at greater; he combines units into tens, tens into hundreds, hundreds into thousands, and thousands into millions. He combines lines into angles, angles into triangles; compares triangles, squares, and circles together; ascertains their peculiar properties and relations; and, from the conclusions he deduces, constructs instruments and ascertains principles which enable him not only to measure the dimensions of this lower world, but the magnitudes and distances of the globes which roll around him in the heavens.

There is no saying at what point the human faculties will stop when once they are aroused to active operation, and stimulated to exert all their energies. We have not only ascertained the bulk of the terraqueous globe, its spheroidal fig ure, its diurnal and annual motions, and the relation in which it stands to other bodies in the universe, but we have determined the dimensions of the solar system, and the distances and magnitudes of most of the bodies it contains, so that we can now speak with as much certainty of the distance of the sun, or of Jupiter and Saturn, as we can of the distance of London from Paris, or of the distances of any two places on the surface of the earth. This is an achievement which at first view might have appeared beyond the power of human genius to accomplish; but by the unwearied observations of modern astronomers, and the application of mathematical principles to such observations, they have been enabled to trace the exact movements of the machinery which is in operation around us, and to determine with precision the relative distance and position of every planet within the system of the There are limits, however, beyond which it is difficult for the human faculties to penetrate. The planetary system comprises an area so vast that imagination is almost lost in the conception. A circle drawn around its circumference would measure more than eleven thousand millions of miles; and a body moving at the rate of thirty miles an hour would require above forty-two thousand years to complete the circuit; still these vast dimensions are within the limits of measurable distance. But when we attempt to pass beyond the boundaries of this system into the illimitable spaces which lie beyond, all our usual modes of computation begin to fail, and the mind is overpowered and bewildered amid boundless space, and the multiplicity of orbs which fill the regions of

sun.

immensity. We can tell that some of the nearest of these orbs are not within a certain distance, but how far they may lie beyond it the most expert astronomer has never yet been able to compute.

The principal mode by which the distance of the fixed stars has been attempted to be determined, is by endeavouring to ascertain whether any of them have an annual parallax. I have already explained the mode by which the distances of the sun, moon, and planets is determined by means of the horizontal parallax, or the angle under which the earth's semidiameter is seen at any of these bodies.* But such a mode is altogether inapplicable to the fixed stars, whose distance from the earth is so great that the horizontal parallax is quite imperceptible. Astronomers have therefore attempted to find a parallax by using the whole diameter of the earth's annual orbit as a base line, namely, one hundred and ninety millions of miles, and endeavouring to ascertain whether any of the fixed stars appear to shift their position when viewed from the opposite extremities of this line. The nature and mode of this investigation will appear from the following explanations:

The axis of the earth extended, being carried parallel to itself during its annual revolution round the sun, describes a circle in the sphere of the fixed stars equal to the orbit of the earth. Thus (fig. 5), let A B C D be the orbit of the earth, S the sun, the dotted lines the axis of the earth extended; this axis, when the earth is at A, points at a in the sphere of the heavens; when the earth is at B, it points at b; when at C, it points at c; and when at D, it points at d; so that in the course of a year it describes the circle a b c d in the sphere of the heavens, equal to the circle A B C D. But although the orbit of the earth, and, consequently, the circle a b c d, be immensely large, no less than many millions of miles in diameter, yet it is but a point in comparison of the boundless sphere of the heavens. The angle under which it appears to an inhabitant of the earth is insensible by any instruments or observations that have hitherto been made, and therefore the celestial poles appear in the same points of the heavens during the whole of the earth's annual course. The star H is nearer the point a than it is to the point c by the whole length of the

* "Celestial Scenery," p. 309-329.