A GIANT SUN. To those who are acquainted with the teachings of astronomy respecting the mighty ruler of our planetary scheme, the title of this essay may appear strange. For assuredly our sun must himself be considered as a giant orb giant in size, as Sir John Herschel says in his charming "Familiar Lectures," and giant in strength, but withal a benevolent giant, being "the almoner of the Almighty, the delegated dispenser to us of light and warmth, the immediate source of all our comforts, and indeed of the very possibility of our existence." How, then, it may be asked, can any other orb be called by way of distinction a giant sun, as though the sun which rules our day were but a dwarf? It seemed fitting that, in speaking of Jupiter in the "Expanse of Heaven," I should describe his mighty orb as a miniature sun; for vast as is the bulk of Jupiter, he seems dwarfed into insignificance when compared with the sun's inconceivably magnificent globe. A thousand Jupiters would not make up the volume of the sun, nor would the mass of a thousand Jupiters outweigh his, if masses so mighty could be balanced against each other. But to speak of any other orb as a giant sun, would seem some such relation to the sun as the sun bears to Jupiter, or Jupiter to the relatively minute orb on which we live. Incredible as the idea of such a globe may be, however, it is with precisely such a globe that I propose now to deal. Mighty as is the orb of the sun, I am to speak of an orb more than a thousand times vaster. Grand as is the scheme ruled by the sun, and inconceivable as are the forces exerted by the sun upon the orbs which circle round him, I am to describe a sun which exerts forces many times more mighty on orbs which themselves probably exceed our sun in mass and volume. Magnificent as is the conception that our sun with his attendant family of planets is sweeping through space at the rate of two or three hundred miles in each minute of time, the sun of which I am about to write carries a far mightier train through space at a rate many times greater. If the reader of these lines had turned his eyes towards the south at about nine o'clock on a clear evening in the beginning of Febuary 1871, he would have seen two orbs which far outshone all others in the heavens. High up in the sky, and not far from the twin stars, Castor and Pollux, the planet Jupiter was shining with a steadfast lustre which distinguished him almost as markedly as his superior brilliancy from all the stars in his vicinity. Low down and almost vertically beneath the kingly planet, was a star which, though not matching Jupiter in actual brilliancy, surpassed him in beauty. For this star-the famous Dog-star of the ancients-glows with a light which continually changes in apparent colour. At one moment it appears unmistakably red, at another a pure green, at another a sapphire blue-though these colours last but for an instant, while, during somewhat longer intervals, the light of the star is white. Poets in all ages have noticed this peculiarity of the light of Sirius, from Homer who compared the fiery lustre of the arms of Diomede with the splendour of the autumn star, "When new risen from the waves of ocean," to our poet-laureate, who sings of Arac and his brothers, that "As the fiery Sirius alters hue And bickers into red and emerald, shone Their morions, wash'd with morning, as they came.” It is difficult to conceive that this orb, brightly as it shines, so far surpasses in volume the magnificent planet which, in 1871, outshone it in the higher heavens, that the very drawing by which astronomers are in the habit of * In the lines referred to Homer seems to describe Sirius as shining more brightly when newly risen than at any other time; and a commentator remarks unhesitatingly, and as though recording some wellattested astronomical fact, that Sirius "shone brightest at its rising." I am not sure that the words of Homer will bear this interpretation, since the word translated "brightly" may equally bear the meaning "splendidly,"—that is, may not relate to the quantity of light actually received from the star, but to the beauty of the star's appearance. It is, of course, not the case that Sirius (either as seen here or in any country) shines most brightly when newly risen; though certainly the star appears more beautiful when near the horizon, its changes of colour being then better marked and succeeding each other more rapidly. A similar remark applies to Arcturus, Vega, and Capella, the three stars which come next to Sirius in brilliancy. Indeed the remark applies to all stars bright enough to shew well through the denser air close by the indicating the insignificance of our earth compared with the sun, might be employed to indicate the inferiority of Jupiter as compared with Sirius. Yet even this fact (for such it is), amazing as it must appear, sinks into insignificance beside the fact that Sirius is a sun many times more splendid than our own. That beautiful star, which even in the most powerful telescope man can construct, appears as a mere point of light, is in reality a globe emitting so enormous a quantity of light and heat, that if it were to take the place of our sun every creature on this earth would be destroyed by its fiery rays. Before proceeding to consider the discoveries relating to Sirius which have rewarded the labours of modern astronomers, it may be interesting to inquire briefly into the ideas of the ancients respecting this splendid orb-the more so that, if we are to accept the descriptions given by ancient writers as literally exact, we must conceive that the star has, during the last two thousand years, undergone a change of the most marvellous kind. It is remarkable that the ancients should have regarded Sirius as comparable with the sun in regard to the influence which it exerts upon the earth. For instance, Sirius was supposed to produce the unhealthy weather prevalent in many parts of Italy during the autumnal months. Yet the influence of the star was not in all countries regarded as baneful; for the Egyptians ascribed the inundations of the Nile to Sirius, and were thus led to worship the star as a deity. The dog-days began at the part of the year when the star rose just as the sky was beginning to grow too bright for any stars to be seen. So that the mischievous effects assigned to these Canicular Days were associated, not with the time when the star shone most conspicuously at night, but with the season when it was known that Sirius was above the horizon in the day-time. But if it is perplexing to understand how the ancients came to regard the rays of Sirius as thus potent, either for evil or for good, it is even more difficult to understand how Manilius was led to anticipate the results of modern astronomical research by boldly suggesting that Sirius is a sun comparable with our own in splendour. Sherburne thus translates the words of Manilius about Sirius :— ""Tis strongly credited this owns a light And runs a course not than the sun's less bright, It seems to cast a dim and weaker ray.” The question whether, as some suppose, Sirius has changed in colour since the days of the ancient astronomers, is of extreme interest and importance. Unfortunately the evidence is far from satisfactory. If the ancients had been a little more careful in describing the phenomena of the heavens, it is probable that many results which are at present being slowly evolved by careful and laborious observation, would admit of being at once and satisfactorily determined. Amongst these must be included the question whether any of the larger stars are changing in colour. Whatever changes are taking place are |