SOLAR ENERGY.

BY A. EMERSON PALMER.

From the astronomer's point of view, the sun is to be regarded in a two-fold aspect. In the first place, it is the center and ruler of our planetary system. In the second place, it is a star, and therefore must be counted as a humble member of that vast company of "envoys of beauty" which come forth every night to "light the universe with their admonishing smile." In the present discussion we are to deal with the sun almost exclusively as the chief of what is termed the solar system. It will be necessary, of course, to make large use of facts and figures which are more or less familiar, and which are, as a matter of necessity, derived from standard works upon solar astronomy.

The sun has, very naturally and quite inevitably, been an object of profoundest interest to mankind from the earliest history of the race. It is as true now as it was when the book of Ecclesiastes was written that "the light is sweet, and a pleasant thing it is for the eyes to behold the sun;" and it was just as true a thousand and ten thousand years before. It is not in the least surprising that in a rude and primitive age men felt impelled to worship the sun. We know to-day better than they possibly could have known that it is far more worthy of adoration and worship than any other physical object within the range of human experience. That men should bow down before the sun, and offer sacrifices to it, and look upon it as a god, is as natural as anything in the world. Το worship mere earthly fire, as some people have done, is to exalt to a lofty place something that is common and insignificant, compared with the majesty, glory, and life-giving power of the mighty-we may almost say the almighty-sun.

Of the sun it may truthfully be affirmed that, while unknown to us in many aspects, it is, nevertheless, well known. Nothing else in the range of astronomy, it is safe to say, arouses so much interest, piques so much speculation, or attracts so many telescopes and other instruments by means of which the astronomer is able to bridge the million-miled chasm dividing us from that which is the source of all that lives, and moves, and has its being on this little planet which we call the earth. This last is the literal fact. Nothing can be more certain that all life on the earth, that every object in the organic world, is absolutely dependent upon the sun. And, more than that, the maintenance of life depends upon the maintenance of the sun's temperature at a substantially uniform degree. If it should grow a little hotter, all living things would be scorched and shrivelled in its fiery breath. If it should grow a few degrees cooler, everything here would be quickly frozen, and the surface of the earth undoubtedly would, in a brief time, be encrusted with ice from pole to pole. We are pensioners upon the sun's bounty far more absolutely than most of us, I imagine, are in the habit of thinking.

THE SUN'S SIZE, DISTANCE, etc.

Not only is all life on the earth due to the sun, but practically all forms of energy known to us are derived from this source. Before proceeding to that phase of the matter, however, let us consider a few of the leading facts that astronomy teaches in reference to the sun, for these are necessary to any clear understanding of the subject. We have to deal here with big figures-so big, in fact, that they can convey no very definite or adequate idea to the average mind.

The distance of the sun from the earth is about 93,000,000 miles. The diameter of the sun is about 860,000 miles. It is necessary to say "about," because, with all the accuracy of astronomical measurements, there is a considerable margin of error. How great it is, or, rather, how small it is, is shown by the remark of Sir John Herschel, that "the recent correction of the solar parallax corresponds to the apparent breadth of a human hair at a distance of 125 feet." The as

tronomers tell us, further, that the quantity of matter in the sun is 330,000 times as great as that in the earth, and that its mean density is one fourth of that of the earth, or one and one-fourth times the density of water; that is to say, the mass of the sun is one fourth greater than would be that of a globe of water of the same size. Put into figures, the mass of the sun is two octillions of tons-the figure 2, followed by twenty-seven ciphers. The force of gravity at the sun's surface is nearly twenty-eight times as great as on the surface of the earth, so that a man weighing 150 pounds here would weigh in the neighborhood of two tons there, and naturally would not cut much of a figure on his feet.

As I said, these numbers are too vast for our minds to grasp them. When I say that the sun is 93,000,000 miles away from us, I really convey no more definite idea to you than if I said 193,000,000 miles-just as if a hundred million miles were of no account whatever! For all practical purposes, either of these dis tances is infinite to us, although in reality the distance of the sun is only a trifle in comparison with that of the far-off fixed stars; so insignificant, in fact, that if I represent the distance of the sun from the earth by the distance from me of a man on whose shoulder I can lay my hand, to indicate proportionately the stupendous distance of the nearest fixed stars, like Sirius for instance, I should have to send the man away from me more than one hundred miles!

SOME CONCRETE ILLUSTRATIONS.

Now let me endeavor to bring some of these figures before your minds in a more concrete form. The diameter of the sun, as I said, is about 860,000 miles. You all know that by traveling steadily one can make the circuit of the earth pretty comfortably in eighty days, or a little less. But going at that same rate it would take not less than twenty-four years to put a girdle around the sun. Still more impressive is another comparison. We know that the distance of the moon from the earth is 240,000 miles. This is something that we can grasp more readily. Now, if the whole interior of the sun were hollowed out and only

the shell remained, and if the earth were then placed at the center of this huge hollow sphere, with the moon still retaining its relative position to the earth -240,000 miles distant--the orbit of our satellite would extend only a little more than half way from the center of the sun to its enormous circumference.

Take, again, the distance of the sun, which, the astronomers tell us, is about 93,000,000 miles. If a man should walk four miles an hour for ten hours a day, and keep it up steadily, it would take him almost three-score years and ten to cover one million miles -sixty-eight and one half years, according to Professor Young; and walking at that speed it would take him more than 6,300 years to reach the sun. Benjamin Franklin was born in 1706. If when he was able to travel alone, say at the age of ten-that is, in the year 1716, the second year of the reign of George I.-he had set out for the sun on an express train running sixty miles an hour, and making no stops for fuel or water, he would be arriving at his destination somewhere in the present year of grace; and at the current rates he would have paid for railway fare something like $2,500,000.

One more illustration before leaving this part of the subject. So far as consciousness reveals it to us, the instant we prick a finger or burn it by bringing it into contact with something hot, that instant we are aware of what has occurred, the intelligence having been flashed along the nerves to the brain. Experiments have shown, however, that impressions travel along the nerves at a definite rate of speed-at the rate of about 100 feet per second. Some one has made the necessary calculation, and asserts that if a child should be born with an arm long enough to enable him to reach the sun, he would not live long enough to know that he had burned his fingers in it, since it would require nearly 150 years for the sensation, coming at the rate of 100 feet per second, to reach his brain.

So much for the mathematics of the case. Enough has been said to show that when dealing with the sun we are dealing with a very big thing, and that its distance from us is prodigious.

A MIGHTY STOREHOUSE OF RADIANT ENERGY.

The sun supplies us with light and with heat, and the sunbeams likewise have the capacity of producing chemical action. But these results are all diverse effects of the same thing. The last word of science on the subject, up to date, is that light, heat, and chemical action are all produced by an "uncomprehended something radiated from the sun." This "uncomprehended something" is termed radiant energy. The sun is a mighty storehouse, an inexhaustible reservoir, of radiant energy, from which, as I said at the beginning, all organic life on the earth is derived.

It requires very little demonstration to prove that substantially all the energy involved in terrestrial phenomena is drawn from this source. The chief forms of energy known to us are water power, wind power, steam power, muscular power, electrical power, and the power of the ocean tides. Every one of these, except possibly the last, is plainly derived from this huge reservoir.

Water falls only because vast quantities of vapor are lifted into the air by the sun, to descend in rain or snow and feed the uncounted streams that flow ceaselessly into the ocean. "All the rivers run into the sea, yet the sea is not full,"* because the energy that comes pouring across 93,000,000 miles of space is constantly at work emptying it. We talk often of the power of gravitation that draws things down: think for a moment of the power of the sun's rays in pulling things up!

Wind, as everybody knows, is only air in motion. How is this motion produced? Here again we must look to the sun for the cause. Heated air expands and rises, and its place is taken by that which is cooler. So motion is established and currents are set up in the atmosphere; and so the wind which turns the arms of the wind-mill, or fills the bellying sails of the ship, or spreads the white wings of the peerless Vigilant all this is seen to be directly due to solar energy.

The same is true of steam power, of muscular pow

* Ecclesiastes, 1, 7.