sides of the case. It is well, however, to remember that Buchanan had at command sources of information, both documentary and legendary, which no longer exist; and if, as is more than probable, the early narratives had acquired colour from the atmosphere through which they had passed, it should not be forgotten that Buchanan was by no means a too credulous historian. He busied himself, as he said, "with our story of Scotland, to purge it of some Inglis lyis and Scottis vanitie." The truth probably lies as usual between the two extremes, and the facts of early Scottish history recorded by Buchanan are neither all false nor altogether true. The most valuable part of the work, however, is that dealing with the historian's own times. He had personal acquaintance with the reigns of four Scottish monarchs, and was an eye-witness of his country's conduct through the crisis of the Reformation. Considerable allowance has, of course, to be made for the religious party spirit which blazed so fiercely at that day, a spirit from which Buchanan, with all his intention to be rigidly just, was by no means altogether free; but with this allowance the later chapters of the great work form one of the most reliable contributions to history.

Buchanan's chief desert of gratitude lies in the fact that he preserved for later days a portrait of times which but for his labour would have been less clearly known. The usual meed of the historian was expected by him-"being assurit to content few and to displease mony." Few, nevertheless, will deny what a eulogist has said of him, that by his scholarly performance and his painstaking he erected "an imperishable monument to the name of Scotland." The story of his life, now seldom perused, must at least continue to illustrate one of the most pregnant periods in the history of his country.

GEORGE EYRE-TODD.

THE SECRET OF THE HEAVENS.

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ANY are the books bearing such titles as "The Wonders of the Heavens," "The Marvels of the Heavens," "Mysteries of Time and Space," "The Story of the Heavens," &c. But few works on astronomy--at least, popular works-make any reference to what may justly be considered as the secret of the heavens. My readers may wonder what is this great mystery which I term the "secret of the heavens." Do not the heavens contain many mysteries? They certainly do. Mystery is attached to many, indeed, we may say, to most, of the heavenly bodies. Even within the bounds of our solar system we have several mysteries. For instance, the constitution of the sun; the real construction of Saturn's rings; the condition of Jupiter's surface, and of the surface of Saturn also; the so-called "canals" of Mars; the origin of the numerous craters which cover the surface of the moon; the constitution of comets ; and other problems, all of which astronomers would like to see solved satisfactorily. When we extend our study to the stars, the mysteries further increase, and the enigmas seem more difficult of solution. We find, for instance, those mysterious objects, the variable stars. I refer especially to those of long period, and some of short period, in which the light is constantly varying. Then we have the "great nebula" in Orion, Andromeda, and Argo, the pale blue objects known as planetary nebulæ, and those still more wonderful systems known as spiral nebulæ. Respecting the real nature of these mysterious bodies, even the spectroscope does not give us much information. It is true that it shows some of these objects to be masses of glowing gas, but it seems as yet impossible to identify some of the bright lines of these gaseous nebula with any known terrestrial substances. It has been established with certainty that hydrogen gas forms one of their constituents, but with reference to the other elements they contain we seem to be still in the dark. But even if we knew their true chemical composition, it would still remain a mystery how they are maintained in a state of glowing incandescence. These and similar mysteries confront us at every step we take, or try to take, in the way of research.

I do not, however, allude at present to any of these mysteries or enigmas. The "secret" I refer to is what I consider to be the great mystery of astronomy. It is this: What is the construction of the starry heavens? What is the relation of the nebulous-looking zone called the Milky Way to the system of brighter stars which stud our midnight sky, and the position of both in space with reference to our sun and solar system? Considering space as infinite-as we seem bound to do-is our visible universe limited, or boundless in extent? These are questions which have hitherto been only partially answered, and they constitute a mystery which may well be termed the "secret of the heavens."

Let us first consider the relation of the Milky Way to our sun and solar system. Accurate observations have shown that the Galactic zone forms very nearly a great circle of the celestial sphere. Most of my readers will know that a great circle" of a sphere means a circle round a sphere the plane of which passes through the centre of the sphere, and divides it into two hemispheres. Now what does this fact regarding the Milky Way denote? It implies clearly that the earth, and therefore the solar system, lies in, or nearly in, the general plane of the Milky Way. This seems to suggest that the sun is closely connected with the Galactic system. The appearance presented by the Milky Way led Sir William Herschel to propose the theory that the vast cluster forming the stellar heavens is shaped like a "disc," or block wheel, the diameter of the "disc" lying in the direction of the Milky Way, and its thickness in the direction of the poles of that zone. This "disc theory," although it was certainly abandoned by its illustrious author in his later writings (as was clearly shown by Struve in 1847, and by Proctor in recent years), has for some reason persistently held its ground in astronomical text-books. It is now, however, considered to be utterly untenable by nearly every astronomer who has studied the subject. An examination of Dr. Boeddicker's beautiful drawing of the northern portion of the Milky Way, recently published, will, I think, be sufficient to convince any reasoning mind that the Galactic zone is not shaped like a disc, and that any little evidence which ever existed in favour of such an hypothesis has now been finally refuted. Possibly the Milky Way may be simply what it seems to be, namely, a vast ring of small stars partially broken up. Its exact construction has, however, yet to be determined. Certain portions of this wonderful zone may perhaps be much nearer to the earth than others; but as we are still ignorant of the distance of any part of it, it is impossible to determine whether its component stars

are of average stellar size, reduced to faintness by immensity of distance, or whether they are really small, and comparatively near us. The late Mr. Proctor favoured the latter view, and I am disposed to agree with his opinion. It is worth noting that the two nearest stars in the heavens-as far as we know at present-Alpha Centauri and 61 Cygni, lie in the Milky Way, and we have really no reason to assume that these stars are very much nearer to the earth than many of the faint stars with which they are apparently associated. The fact that in some binary stars the primary is physically connected with a companion five magnitudes (and even more) fainter than itself, should teach us caution in concluding that a bright star is necessarily nearer to the earth than fainter stars situated in the same region of the sky. Brightness is certainly no test of distance, for we know that 61 Cygni, a star of only the fifth magnitude, is actually a little nearer to us than Sirius, the brightest star in the heavens.

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But even if we knew the exact constitution of the Milky Way, this knowledge would not enable us to satisfactorily answer the question, Is our visible universe finite, or boundless in extent? For even if we knew the exact distance of the Galactic zone, there might still be numerous stars beyond that zone belonging to our sidereal system. We have, therefore, to examine the question from another point of view. There seems to be little doubt that the number of the visible stars is really limited. Most astronomers now admit that the total number of stars visible in our largest telescopes cannot much exceed one hundred millions. This is, of course, a large number, but compared with an infinite number it is really very small. may be proved mathematically-and the demonstration is a very simple one that were the number of stars really infinite, and equally distributed through infinite space, the whole heavens would shine with the brightness of the sun. Far from this being the case, the amount of light afforded by the stars, even on the finest nights, is very small, and the comparative blackness of the background on which they are scattered is sufficiently obvious. The number visible to the naked eye, even with very good eyesight, is not only comparatively but absolutely small. Some unreasoning people think that the number visible in this way is almost "countless," but an attempt to count those distinctly visible in any portion of the sky-for instance, in the "square of Pegasus "-will, I think, convince any intelligent person that the idea is merely an optical illusion, and a popular fallacy which has no foundation in fact. The number visible to average eyesight on an ordinary night does not much exceed 4,000 for both

hemispheres. For exceptionally keen eyesight, and a very clear sky, we may perhaps allow a total of 10,000 for the whole star-sphere, or 5,000 visible from any one place at one time. But surely this is a very small number, scattered over the whole expanse of the heavens. Five thousand men could easily be placed on a small field without touching. Allowing a space of four feet square, or sixteen square feet, for each man—a liberal allowance-I find that over 5,000 men could be placed without touching each other on a field of two acres (a field about a hundred yards square). Now, if we were to rise in a balloon over this two-acre field, we should see a large number of heads, but there would be a lot of ground visible between the heads, and if we rose to a height of, say, two miles, the field would dwindle to a mere speck on the earth's surface.

To show what a limited number even one hundred millions is, I may mention that, from a rough calculation, I find that in a tenacre field of ripe oats the number of grains of corn probably exceeds the number of the visible stars; and we should have to multiply the number of the stellar hosts by at least ten to obtain the number of human beings now living on our comparatively tiny world!

To account for the limited number of the visible stars, some astronomers have suggested that the light of the stars suffers absorption in the ether of space, and that at a certain distance the stellar light must be wholly cut off, so that the most powerful telescope which can ever be constructed by man would fail to pierce through the "cosmical veil" which shrouds the more distant stars from our view. There are, however, several objections to this hypothesis. I will mention one or two. M. Celoria, using a small telescope of power barely sufficient to show stars to the eleventh magnitude, found that he could see almost exactly the same number of stars near the northern pole of the Milky Way as were visible in Sir W. Herschel's large telescope, showing that here, at least, no increase of optical power will materially increase the number of stars visible in that direction, and that probably very faint stars do not exist in this region of space. Sir John Herschel, speaking of his observations at the Cape of Good Hope, says, "We are not at liberty to argue that at one point of its circumference our view is limited by this sort of cosmical veil which extinguishes the smaller magnitudes, cuts off the nebulous light of distant masses, and closes our view in impenetrable darkness, while at another we are compelled by the clearest evidence telescopes can afford to believe that star-strewn vistas lie open, exhausting their power and stretching out beyond their utmost reach, as is proved by that very phenomenon which the existence of such VOL. CCLXXIII. NO. 1939.

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