the temperature; and, at certain heights, perpetual ice and snow.

3. Ascents into the higher regions of the atmosphere by means of those balloons, in drawing your attention to which I began my present volume, discover the same truth; that is, that the higher we ascend, or the further we leave below us that denser atmosphere which immediately adjoins the sea and the lower levels of the land, the colder we find the temperature, and the less discoverable heat accompanying the sun's light.

4. But, as opposite facts, in the Arctic regions, and in other situations of which the atmosphere is still comparatively dense or thick, while we stand upon beds of ice, that are neither melting or likely to melt, except upon the surface, we are often scorched by the heat that we find accompanying the light of the summer's sun. The heat, therefore, is in the atmosphere of the earth, and not in anything which flows to us from the sun.

5. And yet, my little readers, we are all apt to fancy, and the world has ever been apt to fancy, that the heat which we feel in the presence of the sun's light, (though we often feel heat also in its absence,) must needs come to us from the sun, in company with its light; or, in short, that the light of the sun is the light of a fire; that the sun is a fire-a disc or a globe of fire; and further, that the sun being a fire, it is a fire which must one day burn itself out;-that its heat must diminish or decay;-that it is a burning substance which must at last burn itself out!

6. But it will be plain to you, that, were there anything like truth in these representations, the very reverse of what I have been mentioning must happen. You know that the nearer you approach to a fire, the hotter you find your place; whereas, I have assured you experience shows, that the nearer we approach to the sun, (that is, the further we go from the centre of the earth, even with the sun over our heads,) the colder is our situation!

7. That the sun gives light; that it is a luminous or shining body; and that, in some manner, its action upon our atmosphere (an action effective in proportion to the density of the atmosphere) produces the atmospherical heat of which we know so well the experience; these things are certain. But the sun, though luminous, is not fiery; though shining, it is not fire. The sun is no burning disc, nor burning globe; it is in no danger of burning itself out; and it has no heat, nor any material of heat, respecting which there is the least danger that it will either fail or lessen.

8. In truth, it is at present supposed by some, that the light and heat of the sun are to be ascribed only to electrical causes. You must hereafter make yourself acquainted with what is electricity.

QUESTIONS.

1. Do we find the air the colder, even in the midst of the brightest sunshine, the higher we ascend from the level of the sea, or of the

sun?

plains; though in so doing, we ascend by so much the nearer to the 2. Are the tops of very high mountains covered with perpetual snow? 4. In some situations, do we feel excessive heat under the sun, even while we are standing upon ice which nevertheless continues unmelted? 5. Has it been fancied that the fire of the sun is likely to burn itself out? 6. What contrast may be observed between the effect of drawing nearer to a fire, and that of drawing nearer to the sun? 7. Is the sun, nevertheless, the certain though hidden cause of the light and heat which we enjoy? Is it plain, that, to whatever changes the sun may really be liable, there is no reason to suppose that either its light or heat are liable to progressive extinction or decay? 8. Do some ascribe the light and heat of the sun only to electrical causes?

CHAPTER XV.

PARLEY TALKS OF THE LIGHT OF THE SUN, AND OF THE SUN'S SPOTS.

1. THE intensity of that light which covers the face of the sun, and which the sun diffuses through our atmosphere, may be partly judged of by comparing it, in both instances, with the amount and the influence of the light of the moon. We can look at the moon, but we cannot look at the sun; and the light of the moon, though brilliant, yet leaves the atmosphere so dark that it interrupts our view, neither of the light of the stars, nor of the deep colour of the surrounding sky. In general, while the sun shines, the sky appears to us but of a light azure, and we see nothing of any heavenly body but itself; though sometimes the moon, and sometimes one or other of the planets, form an exception to the rule.

2. The cause, in the meantime, of the sun's luminosity, remains unconjectured, or not so conjectured as to satisfy our minds. It is not fire, but what then is it else? Is the sun luminous throughout; or, has it luminous clouds, or a luminous atmosphere only, with a dark and solid body beneath?

3. Sir William Herschel was of opinion, that the sun consists of a dark opaque body or nucleus, in the atmosphere of which float luminous clouds that compose its shining matter. The inferior brightness, and, at the same time, the uniformity of colour of these shallows, he explained by supposing that these clouds consist uniformly of two strata, of which the uppermost or outermost is almost immeasurably the brightest; while the lower, or inner stratum, or that nearest to the dark body of the sun, is of very inferior lustre.

4. Leaving, however, these things as unsettled as I find them, I shall only tell or remind my little readers, that the sun is not even that uniform ball or disc of light or fire which it seems to their eyes; but that, in spite of all its dazzling golden lustre, it has spots and variations of light and figure upon its face, like the face of the moon; though none of them of that permanent character which enables us to draw a map of the sun in the same manner that we draw, and that I have exhibited to you, in a former chapter, a map of the moon.

5. Still, I venture to show you, now, a figure of the disc of the sun, darkened with large spots; but, in the disc of the sun, the number, and the figure, and the

size, and the place of all the spots, are in constant variation. They are sometimes so large as to be seen with the naked eye. Herschel, in the year 1779, observed

one which was about fifty thousand miles in diameter; or more than six times the diameter of the earth.

6. The changes of place, size, and figure, appear to depend, in part at least, upon the rotation of the sun. For they are thought not to move round the sun, but with the sun. If, then, the spots were permanent, the same spots ought to return at regular intervals, and we ought to be able to draw maps of the two hemispheres of the sun, like those we draw of the two hemispheres of the earth.

7. The spots, if observed for two or three days in succession, seem to have moved, during that time, from east to west, across the body of the sun; but this (the

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