with the pressure. When temperature has attained a certain point, the properties of a liquid and those of the vapour continually approach to similarity, and above a certain temperature the properties of a liquid are not separated from those of a vapour by any apparent difference between them. Hence, the gaseous and liquid states are only widely separated forms of the same condition of matter, and pass into each other without any interruption or breach of continuity. In one way you can see this, in another you cannot. Begin, for example, with water take this path B, a, A; return by A, a, B. We begin with water at B, we have water and saturated steam about a, then superheated steam till we reach A. On our way back we have no such stages-though when we reach B there is water as at first.1

Potassium and sodium are somewhat remarkable: these metals are near akin in their specific gravities, their atomic weights, their chemical affinities, and the properties of their compounds. Potassium melts at 136°, sodium at 19°, but the alloy or mixture of the two is liquid at the ordinary temperature of the air. Cold is made to exist amidst hottest fire, and ice may be taken from a burning crucible. These are facts which only experiment could discover, and can only be reduced to law by a formula which includes both the usual course and the apparent exception. Observe more particularly as to water when in contact with ice it cannot be cooled below

zero without being converted into ice. In heating the water the ice melts, but the temperature of the mixture is never raised above o° so long as the ice remains unmelted. Hence, the water contains a greater quantity of heat at o° than ice contains at o°, and gives up its heat to become ice. We do not know what becomes of this heat-nor how to account for the fact that water at o° is not ice, and that ice at o° is not water.

Physicists state that changes in consciousness are correlated with molecular motions of nerve matter, which are highly differentiated forms of solar radiance. Waves of this radiance speed to the earth at the rate of more than five hundred trillions to the second; and impart their energy so that we 1 "Recent Advances in Physical Science," p. 335: Prof. P. G. Tait.

have growth of grass. Cattle browse on this, and hold in another form of equilibrium, by integration of tissues, these metamorphosed sunbeams. Man, assimilating the nitrogenous tissues of the cow, builds up that wonderful white and grey nerve-tissue by which is obtained the astonishing and completed transformation of solar radiance into human consciousness. We know of nothing more wonderful than this continual miracle: a miracle of progress by daily infinitesimal steps and transformations, and without our being able to say -"there is the place of birth." It is certain that a series of actions, displayed by the various tribes of the animal kingdom, may be so placed that they form one whole; of which it is impossible for the human intellect to resolve the complex into the more simple. That is not all: mental life comes out of physiological life, but how mental activity was originated in organisms by the simple elementary modifications of external to internal relations, and passed from the automatism of lowest creatures to the highest act of consciousness in man, is a mystery; nor can we say where intelligence begins, nor when

"turned the dense black element Into a crystal pathway for the sun."

We can think of a world, all dark, beginning to vibrate differently and in various rapidities until all gorgeous colours shine in light and beauty; or we may conceive, as to the low rumblings of many motions requiring tone until every musical note vibrates in world-wide oratorio; so miraculous and varied is that operation by which, from things dark and silent, God brings the light of human intellect, and the many prayers and praises which make the earth a vast cathedral.

Of the innumerable combinations of matter and incarnations of energy which are going on all around us, we only know a few of the simplest; what then

“In yonder hundred million spheres ?”

Turn to the exactest of all sciences, Astronomy. What is revealed? The diamond dust in the sky becomes suns and stars. Little cloudlets expand and reveal worlds of majesty. There are variable suns, binary and multiple systems, stars suddenly blazing forth in splendour, and mys

Astronomical Varieties.

399 terious dark orbs rolling in night. Great is the variety of the stellar system; yet not a tithe of the various orders of bodies are known; we have only a faint conception of the wonderfully varied forms of creation within the stellar spaces. Not long ago, astronomers could scarcely allow that the vast depths, wherein the planets pursue their career, are the home of countless smaller bodies rushing in wide orbits round the solar mass. Few or none believed that those faintly gleaming lights, passing with silent swoop across a star group, leaving no trace of their existence and seeming of as little importance in the universe as a rain-drop or snow-flake, indicated the close of a career which had often, by uncounted millions of miles, surpassed the utmost limits of the known planetary system. These crowds of independent orbs, rushing disorderly round the sun, in no sort an obedient family, would, it was considered, make the sweet bells of the planetary system to jangle, be out of time, and harsh: nevertheless, the earth, sweeping on in her path, is exposed to cannonade from more than a hundred meteor systems; and at critical periods is assaulted with heavier metal than that encountered in the second week of November: not only balls weighing many pounds, but of several tons, have been shot against her.

How wonderful are the coloured suns! The brilliant Vega, a splendid steel-blue star, in the constellation Lyra, at midnight in winter, and earlier with the approach of spring, as it skirts the southern horizon, scintillates with red, blue, and emerald light. Arcturus, low down in the east and northeast, in spring evenings twinkles yet more beautifully. Capella, towards the north, in summer nights, notably sparkles. Sirius, noblest of all

"The fiery Sirius alters hue, And bickers into red and emerald."

These various colours are caused in part by our own atmosphere; but the stars are not wanting in real colours of their own. Sirius, Regulus, and Spica are white stars; Betelgeux, Aldebaran, Arcturus, and Antares are red; Procyon, Capella, and the Pole-star are yellow; Castor is of slightly green tint; Vega and Altair are bluish: Castor has a green companion, Antares also, and there is the well-known "garnet-star."

In the double, triple, and multiple stars are many of the tints of the rainbow. "Here we have a green star with a deep blood-red companion, there an orange primary accompanied by a purple or indigo-blue satellite. White is found mixed with light or dark red, purple, ruby, or vermilion." One of the most startling facts is their colour is not unchangeable. Of old, Sirius was red, now it is white. A double star in Hercules changed in twelve years "from yellow, through grey, cherry-red, and egregious red, to yellow again." These show that the stars are formed of different elements, and that their vapours burn with variable brilliancy. There is Mira, the marvellous, shining brightly for two days, thirteen hours and a half, as a star of the second magnitude; then, suddenly losing her light, in three hours and a half falls to the fourth magnitude; then, the brilliancy growing, in another three hours and a half she reattains her former lustre. The times of at least twentyfour variable stars have been calculated. Sometimes, as in the case of temporary stars, a spectrum of the fourth class is suddenly crossed by the bright lines of hydrogen, showing either a last discharge of red flames, or a flicker due to some last chance impact of meteoric matter.

Suns far off in space, and, for aught we know, important as our own, quickly blaze with wonderful brightness, and afterwards lose their splendour. A beautiful star appeared in Cassiopeia, A.D. 1572. It surpassed all other stars, was as Venus at her brightest, became of the first magnitude, exhibited various hues, and disappeared in March 1574. In May 1866, a star which had long shown feebly in the constellation of the Northern Crown, suddenly burst into flames, and attained the glory of a second magnitude star. Scientific men thought that the hydrogen encircling it passed from a relatively cool state, like that surrounding our sun and Capella, and Aldebaran, into intense heat, which made it glow with a hundredfold brightness. It is now, again, a star of the tenth magnitude. "For the years A.D. 807, 849, 1096, and 1607, and several others . . . a great deficiency of the sun's light has been recorded. Thus in the annals of the year A.D. 536, the sun is said to have suffered a great diminution of light which continued fourteen months. From October, A.D. 626, to the

following June, a defalcation of light to the extent of onehalf is recorded; and in A.D. 1547, during three days, the sun is said to have been so darkened that the stars were seen in the day-time." 1

We can study, not only changes in splendour, and fatal catastrophes, and the succession of phases of life in one particular star, but different simultaneous phases in many: some stars starting into life, others becoming older, others older and older, sometimes a dead star-a star scarcely noticeable by the astronomer; and the dead sometimes lives again. One, lately examined by Dr. Huggins, was a star which had cooled down to its lowest stages; but it became bright by an outburst of hydrogen. Does all this, like the rolling of the ocean, rhythmically repeated yet ever varying, while it rivets our attention and hurries us along, leave a final impression of solitude on the mind? No: the motions of the stars, orderly and stately in gorgeous hue, bear down into the beholder's soul conceptions of hitherto unimagined glory and beauty.

Take our own system: the rule of law within may itself be regarded as a miracle, if wrought by chance. The chances against the uniformity being by chance are, Laplace states, four millions of millions to one. The movement of the sun on its axis, of the planets round the sun, of the satellites round their primaries (those of Uranus, possibly Neptune, excepted), and the motion of all on their axis, is from west to east. There is nearly a regular gradation in their density, and the distances are curiously relative, weaving them into one web of mutual arrangement and harmonious agreement. Nevertheless, the uniformity is not an invariability impressed and stamped by unintelligent force. Variety prevails everywhere. Take the rates of axial rotation. The sun revolves in about twenty-five days eight hours; the moon requires a month to turn in; the earth occupies one day; Mercury, twenty-four hours and five minutes; Venus about twenty-three hours and a half; Mars, somewhat more than twenty-four hours and a half; Jupiter, less than ten hours; and Saturn, say, ten and a half hours. We are sure that there is reason in all this: for

1 "Outlines of Astronomy: Sir John F. W. Herschel, Bart.