but most of them agree that no isolated stars of a blue, or green, or purple colour can be seen even with powerful telescopes. So commonly has this been asserted, that the late Admiral Smyth, who thought he could recognise very decided blue tints among the minuter stars, expressed a doubt whether this might not be due to some idiosyncrasy of his eyesight. And certainly there is no instance, among the thousands on thousands of stars whose places have been recorded, of one isolated star of a well-marked blue colour.

But when we turn to those interesting objects, the double stars, the scene is wholly changed. Every variety of colour is seen among these singular systems. We not only find all the tints of the rainbow, but a number of other colours, such as fawn, buff, ashcolour, silvery white, coppery, and grey. The range of colour seems, in fact, wholly unlimited; and astronomers need the aid of a practical artist before they can even tabulate the long list of colours which the double stars exhibit to them.

There are few subjects which seem better calculated to attract and interest even the least thoughtful than the presence of these singularly beautiful colours among the orbs of heaven. Regarding the fixed stars as suns, the centres of schemes of dependent worlds resembling in many respects the worlds which circle around our sun, we cannot but look with wonder upon the strange scene which must be presented amid those distant systems. It would be interesting enough to consider merely the case of a number of worlds circling around

a red, or orange, or yellow sun. But when we imagine the condition of those worlds which travel round a pair of differently-coloured suns, we are lost amid the perplexing considerations which suggest themselves. 'Imagination fails to conceive,' says Sir John Herschel, 'the charming contrasts and grateful vicissitudes of a red and green day, alternating with white light or with darkness, in the planetary systems belonging to these suns.'

Perhaps, however, we do not see in this description the true result of the presence of two suns as the companion rulers of a planetary scheme. Until we know • something of the distance at which the members of such a system circle around their double primary, we can hardly assert with confidence that those planets have days of different colours. It may well be that they are so far from both the orbs which sway their motions that their two suns are always seen close together, as they appear to us, who are so much farther off.

But even when we take this. view, we are struck with the thought of the strange scene which the sky of one of those distant planets must present. Conceive two coloured suns above our horizon. Now one, now the other, is the leading light of the firmament. Their distance from each other is constantly varying as the planet circles round them. Often one must pass before the other, and then the colour of the day changes, passing through many gradations, as the strange transit of sun over sun is in progress. Then every object on such a planet must cast two different

shadows. If the suns are red and green, for instance, the shadows are green and red. When we remember how large a part shadows play in the appearance of a landscape, we see at once how strange a scene the hills and dales and valleys and woods in those distant worlds must present to those who inhabit them. Living creatures must exhibit a yet stranger aspect.

But our object is not to deal with fanciful speculations such as these. There is a real physical meaning double stars which is well worth

in the colours of the

searching out.

Let us first notice certain facts about the colours of the double stars which are at once interesting and instructive.

In the first place, it has long been noticed that among many double stars complementary colours may be recognised. Red and green companions are commonly met with; in some instances the beautiful contrast between yellow and purple is exhibited ; while not unfrequently blue and orange stars are seen in company.

It was suggested that this peculiarity might in reality be optical rather than real. It is well known that where the brighter of two neighbouring objects presents a well-marked colour, the fainter very commonly presents the complementary colour, though not in reality tinted with that hue. Artists are familiar with this peculiarity, insomuch that some of the most striking effects of colour in well-known paintings, have been produced, not by a real intensity in the colours

Many of our readers have

made use of, but by the judicious contrast of suitable complementary colours. doubtless heard the story of the French painter who tried in vain to obtain a certain brilliant yellow tint, which he was desirous of introducing into a picture, and was about to set out for the Louvre, to see how other painters had mastered the difficulty, when a passing cabriolet, the yellow wheels of which were picked out with purple, showed him how he could give brilliancy to the yellows he had been so little satisfied with. Thus astronomers thought the green companions of brilliant red stars, or the blue companions of brilliant orange stars, might be in reality simply white stars whose purity of tint was overmastered by the effect of contrast.

But this idea had to be abandoned. It was found possible in several instances to hide the brighter of the two stars from view while the smaller still continued visible. When this was done there remained, of course, no effect of contrast. Yet in nearly every instance the colour of the smaller star continued as well markedthough not perhaps as pleasing-as when both stars were visible together. Usually this plan of hiding one star while the other continued visible was effected by artificial means, a small cross-bar of brass or copper being introduced into the telescope's eye-piece for the purpose. But there is one instance in which the moon was made to aid the astronomer; and the story seems to us so interesting that we venture to give it in full:

:

The star Antares, or the Scorpion's Heart, had long been a source of perplexity to astronomers. It is a brilliantly-red star, and has indeed been called the Sirius of red stars. But when the star is watched intently, especially with an instrument of adequate power, a singular scintillation of green light is found to obtrude itself most persistently into notice. It was suspected, at length, that this star must have a green companion; but for a long time none could be found. At length the late General Mitchell, with the fine telescope of the Cincinnati Observatory, detected a companion to the brilliant Antares; and, as had been suspected, this companion proved to be green. This, the first noteworthy achievement of the Cincinnati telescope, was a source of considerable gratification to Mitchell, until he heard that at another observatory two green companions could be seen. He searched again and again for the second green star, but could find no trace of it; and at last the welcome news came that the telescope of the other observatory was in fault. It possessed the undesirable faculty of dividing small stars on its own account-that is to say, it divided stars which really were single. Reassured of the fidelity of his telescope, General Mitchell reexamined the star. But he, and others who joined in the work, found it difficult to satisfy themselves as to the real greenness of the companion. The latter also was too minute an object, and too close to its primary, to be separated by the artificial device mentioned above.