The race, then, to whom we owe the general system of constellations, was probably one with so much talent for artistic delineation that in later ages this people would have become distinguished for skill in painting and sculpture. I think the sculptures found in Babylon, and the traditions left of the artistic skill of the Babylonians, correspond well with the belief that the constellations had their origin, and astronomy its first development, among that people or a kindred race.

But the chief lesson to be derived (and I think it may fairly be derived) from the study of the constellation-groups is, that enough resemblance still remains, if only the arbitrary boundaries invented for the constellation figures in recent times are overlooked, to assure us that no very great changes have taken place in the aspect of the heavens for thousands of years. A few stars here and there have certainly changed greatly in brightness, and some few have changed considerably even in position; while a considerable number have probably changed slightly in brightness, and all, or very nearly all, have changed somewhat in position. But on the whole the aspect of the stellar heavens now is the same as it was when the constellation figures were first imagined.

This thought not only assures us of the permanence of our own sun (seeing that among the thousands of his fellow-suns which spangle the heavens so few have changed in lustre), but seems to me to give to the study of the stars a singular charm. Our antiquaries and archæologists present for our study the relics of long past ages, and we may often rest assured that the objects thus gathered for us were really used in old times, though probably in a manner not understood by us, and when in a condition very unlike that in which they have reached our times. In nearly all such instances, however, doubt exists as to the antiquity of the relic, as to the race to whom it really belonged, and as to its real use and purport. But as regards the stellar heavens we have no doubt. Of all the objects on which the eyes of remote races have rested, the celestial bodies are undoubtedly the most ancient, while at the same time they and they alone were most certainly contemplated by all mankind. From the very earliest ages, from the time when the child-man first turned his thoughts from mere animal wants to the wonders of nature, the stars, and the sun and moon and planets must have drawn to themselves the attention of all who had eyes to see even though they had no power to understand the glories of the star-depths. Men pictured among the stars the objects most familiar to them, the herds and flocks which they tended, the herdsman himself, the waggoner, the huntsman, the birds of the air, the beasts of the field, the fishes of the sea, the ship, the altar, the bow, the arrow, and, one may say, all that according to their knowledge existed in the heavens above, in the earth beneath, and in the waters under the earth. Imperfect and anomalous as these meanings are, in relation to modern astronomy, with its exact methods, elaborate instruments, and profound investigations into the meaning of all the phenomena of the heavens, they nevertheless retain their place, and are likely long to do so, in virtue of the hold which they took, in remote ages, on the imagination of mankind in general.

XIII.
TRANSITS OF VENUS.

As a transit of Venus, visible in this country, occurs in December, 1882, my readers, although they may not care for an account of the mathematical relations involved in the observation and calculation of a transit, will probably be interested by a simple explanation of the reasons why transits of Venus are so important in astronomy.

Of course it is known that a transit of Venus is the apparent passage of the planet across the face of the sun, when, in passing between the earth and sun, as she does about eight times in thirteen years, she chances to come so close to the imaginary line joining the centres of those bodies that, as seen from the earth, she appears to be upon the face of the sun. We may compare her to a dove circling round a dovecot, and coming once in each circuit between an observer and her house. If in her circuit she flew now higher, now lower, or, in other words, if the plane of her path were somewhat aslant, she would appear to pass sometimes above the cot, and sometimes below it, but from time to time she would seem to fly right across it. So Venus, in circuiting round the sun, appears sometimes, when she comes between us and the sun, to pass above his face, and sometimes to pass below it; but occasionally passes right across it. In such a case she is said to transit the sun's disc, and the phenomenon is called a transit of Venus. She has a companion in these circuiting motions, the planet Mercury, though this planet travels much nearer to the sun. It is as though, while a dove were flying around a dovecot at a distance of several yards, a sparrow were circling round the cot at a little more than half the distance, flying a good deal more quickly. It will be understood that Mercury also crosses the face of the sun from time to time—in fact, a great deal oftener than Venus; but, for a reason presently to be explained, the transits of Mercury are of no great importance in astronomy. One occurred in 1861, another in 1868; another in May, 1878; yet very little attention was paid to those events; and before the next transit of Venus, in 1882, there will be a transit of Mercury, in November, 1881; yet no arrangements have been made for observing Mercury in transit on these occasions; whereas astronomers began to lay their plans for observing the transit of Venus in 1882, as far back as 1857.