her breast against a thorn, but rather an ecstatic strain from a soul so full it must tell its rapture or die. Its charm was past all telling, beyond the reach of words. Still, as I write, hundreds of miles away, after months of rapid travel, my heart thrills with the echo of its ineffable. sweetness. The doe (the winsome thing, with the haunting eyes) leaned heavily against my arm while we stood and listened. Night was fallen, for in these latitudes it makes brief mingling with day. It is only to meet and kiss in a crimson blush and part again. "Good-by forever," we said, as the lock snapped in the iron valves. The voice of the bulbul followed us through the perfumed dusk, like an invisible angel allowed to pass the guarded gates of Eden and cheer the homely pilgrims on their way.

Freshly the breeze blew, and the briny smell of the sea was tonic, after the languors of the palace. The rich and balmy eve invited to silence. Under a trance we floated between blue and blue (whether in the body or out of the body I cannot tell) in the supreme delight of a day unreal in its poetic lights, so like the stuff which dreams are made of, I sometimes wonder which was dream and which reality.

THE HEAT AND LIGHT OF THE SUN.

C. A. YOUNG.

[Charles Augustus Young, the astronomer, was born in New Hampshire in 1834. He has been professor of mathematics and astronomy in several Western colleges, and in 1877 became professor of astronomy at Princeton College. His spectroscopic studies, and researches into the physics and chemistry of the sun, are of high scientific value. He

has written much on scientific subjects, his principal work being "The Sun," from which we extract some interesting passages.]

SUNLIGHT is the intensest radiance at present known. It far exceeds the brightness of the calcium-light, and is not rivalled even by the most powerful electric arc. Either of these lights interposed between the eye and the surface of the sun appears as a black spot upon the disk.

We can measure with some accuracy the total quantity of sunlight, and state the amount in "candle-power:" the figure which expresses the result is, however, so enormous that it fails to convey much of an idea to the mind: it is 1,575,000,000,000,000,000,000,000,000; fifteen hundred and seventy-five billions of billions, enumerated in the English manner, which requires a million million to make a billion; or one octillion five hundred and seventy-five septillion, if we prefer the French enumeration.

The "candle-power," which is the unit of light generally employed in photometry, is the amount of light given by a sperm-candle weighing one-sixth of a pound and burning a hundred and twenty grains an hour. An ordinary gas-burner, consuming five feet of gas hourly, gives, if the gas is of standard quality, from twelve to sixteen times as much light. The total light of the sun is, therefore, about equivalent to one hundred billion billion of such gas-jets..

Thus far we have considered only the total light emitted by the sun. The question of the intrinsic brightness of his surface is a different though connected one, depending for its solution upon the same observations, combined with a determination of the light-radiating areas in the dif ferent cases. Since a candle-flame at the distance of one metre looks considerably larger than the disk of the sun, it is evident that it must be a good deal more than seventy thousand times less brilliant. In fact, it would have to be

at a distance of about 1.65 metres to cover the same area of the sky as the sun does, and therefore the solar surface must exceed by a hundred and ninety thousand times the average brightness of the candle-flame. . . .

One of the most interesting observations upon the brightness of the sun is that of Professor Langley, who a few years ago (in 1878) made a careful comparison between the solar radiation and that from the blinding surface of the molten metal in a Bessemer "converter." The brilliance of this metal is so great that the dazzling stream of melted iron, which, at one stage of the proceedings, is poured in to mix with the metal already in the crucible, "is deep brown by comparison, presenting a contrast like that of dark coffee poured into a white cup." The comparison was so conducted that, intentionally, every advantage was given to the metal in comparison with the sunlight, no allowances being made for the losses encountered by the latter during its passage through the smoky air of Pittsburg to the reflector which threw its rays into the photometric apparatus. And yet, in spite of all this disadvantage, the sunlight came out five thousand three hundred times brighter than the dazzling radiance of the incandescent metal. . . .

If the amount of solar light is enormous, as compared with terrestrial standards, the same thing is still more true of the solar heat, which admits of somewhat more accurate measurement, since we are no longer dependent on a unit so unsatisfactory as the "candle-power," and can substitute thermometers and balances for the human eye.

It is possible to intercept a beam of sunshine of known. dimensions, and make it give up its radiant energy to a weighed mass of water or other substance, to measure accurately the rise of temperature produced in a given

time, and from these data to calculate the whole amount of heat given off by the sun in a minute or a day.

Pouillet and Sir John Herschel seem to have been the first fairly to grasp the nature of the problem, and to investigate the subject in a rational manner.

Herschel preferred to express his results in terms of melting ice, and put it in this way: the amount of heat received on the earth's surface, with the sun in the zenith, would melt an inch thickness of ice in two hours and thirteen minutes nearly.

Since there is every reason to believe that the sun's radiation is equal in all directions, it follows that, if the sun were surrounded by a great shell of ice, one inch thick and a hundred and eighty-six million miles in diameter, its rays would just melt the whole in the same time. If, now, we suppose this shell to shrink in diameter, retaining, however, the same quantity of ice by increasing its thickness, it would still be melted in the same time. Let the shrinkage continue until the inner surface touches the photosphere, and it would constitute an envelope more than a mile in thickness, through which the solar fire would still thaw out its way in the same two hours and thirteen minutes, at the rate, according to Herschel's determinations, of more than forty feet a minute. Herschel continues that, if this ice were formed into a rod 45.3 miles in diameter, and darted toward the sun with the velocity of light, its advancing point would be melted off as fast as it approached, if by any means the whole of the solar rays could be concentrated on the head. Or, to put it differently, if we could build up a solid column of ice from the earth to the sun, two miles and a quarter in diameter, spanning the inconceivable abyss of ninetythree million miles, and if then the sun should concentrate his power upon it, it would dissolve and melt, not in an

hour, nor a minute, but in a single second: one swing of the pendulum, and it would be water; seven more, and it would be dissipated into vapor.

In formulating this last statement we have, however, employed, not Herschel's figures, but those resulting from later observations, which increase the solar radiation about twenty-five per cent., making the thickness of the ice crust which the sun would melt off of his own surface in a minute to be much nearer fifty feet than forty.

To put it a little more technically, expressing it in terms of the modern scientific units, the sun's radiation amounts to something over a million calories per minute for each square metre of his surface, the calory, or heat-unit, being the quantity of heat which will raise the temperature of a kilogramme of water one degree centigrade.

An easy calculation shows that to produce this amount of heat by combustion would require the hourly burning of a layer of anthracite coal more than sixteen feet (five metres) thick over the entire surface of the sun,-ninetenths of a ton per hour on each square foot of surface,-at least nine times as much as the consumption of the most powerful blast-furnace known to art. It is equivalent to a continuous evolution of about ten thousand horsepower on every square foot of the sun's whole area. As Sir William Thomson has shown, the sun, if it were composed of solid coal and produced its heat by combustion, would burn out in less than six thousand years.

Of this enormous outflow of heat the earth of course intercepts only a small portion, about 2.200.000.000. But even this minute fraction is enough to melt yearly, at the earth's equator, a layer of ice something over one hundred and ten feet thick. If we choose to express it in terms of "power," we find that this is equivalent, for each square foot of surface, to more than sixty tons raised to the