the distance of the Sun from the Earth was determined to be 95,370,000 miles. This was accepted as correct; it went into school books and general literature, and remained unquestioned for thirty years.

But Hansen, another German astronomer, after long and careful study of the perturbations of the Moon, announced, in 1854, that the lunar phenomena cannot be explained on the basis of the observations of 1769, and the calculations of Encke, and that an error existed equal to about one thirtieth of the whole distance of the Sun. This statement has been amply confirmed; and to correct the error requires a reduction of the assumed dimensions of the entire solar system. Still, a problem of such importance is worthy of repeated efforts; modern science is content with nothing which falls short of absolute certainty.

In December, 1874, another transit of Venus occurred; and preparations more extensive and elaborate than before were made to observe it. Observations were made by American astronomers at eight different places, all of which are in foreign countries, the transit being invisible on the American continent. Doubtless valuable results have been secured, and will soon be added to our current knowledge; but so much of time and labor is required for comparison of observations, and for mathematical calculations, and so great the honorable ambition of each corps of scientists to do accurate and reliable work, that, so far as we know, no authoritative and final report has yet been made.

Meanwhile the great question has been attacked in two other ways. One is the method indicated by Hansen, which depends on the gravitating force of the Sun upon the Moon. The other seeks to ascertain the velocity of light, which is known, by observations of Jupiter and his moons, to pass from the Sun to the Earth in eight minutes and eighteen seconds. The results of investigation by these two methods do not wholly agree with each other, yet they approximate, indicating an error of about three million miles in the distance of the Sun as calculated by observing the transit of Venus in 1769.

If the recent transit should confirm this correction, quite a long list of new figures must be substituted for those which older scientists have been quoting all their lives. If we are

three million miles nearer the Sun than we calculated, then the Sun's diameter is about thirty thousand miles less than we concluded it; and Mercury and Venus, and all the planets, are nearer the Sun and all are smaller than we thought them, except the Earth, whose magnitude is ascertained by other methods. The reduction of one thirtieth goes through the whole column. Professor Newcomb regards the new measurements as more reliable than the older, and accordingly adopts them in his description of the solar system.

One of the most interesting applications of the methods of celestial measurement is in the attempt to ascertain the distances of the fixed stars. This problem is far more difficult than the one already described. Professor Newcomb states that, "so far as is known, and beyond all reasonable doubt, the nearest fixed star is a Centauri," a constellation of the Southern Hemisphere. The conclusion from a long series of the most careful observations, made with the best instruments, is that the pair of stars which are marked Alpha on the maps of the constellation named are distant from us two hundred and twenty-six thousand times the distance of the earth from the Sun. Stated in miles, this is more than twenty millions of millions. Assuming that the investigations of the French scientists have really discovered the velocity of light, estimating it to be one hundred and eighty-six thousand miles in a second of time, this double star, the nearest neighbor of the solar system, is so far away that the rays which enter our eyes as we look upon it have been three years and one hundred and fifty-five days upon their stupendous journey.

The disciples passing out of the magnificent temple which crowned Mount Moriah, and turning to admire and wonder, said, "Master, see what manner of stones and what buildings are here!" What language shall utter our thought as we survey the vast proportions of God's universe?

As the

A traveler, making a journey by night, looks out of the window of the car, and sees a light some distance from the road, but how far he does not for a moment know. But he knows that the track runs for miles in a straight line. rapid train advances, the light seems to swing around toward the rear of the train. The rapidity with which it swings toward the rear furnishes a criterion by which to judge of its disFOURTH SERIES, VOL. XXXI.-17

tance. If a few seconds send it out of sight, the light is not far from the railroad. If at the distance of a mile from the first point of observation the traveler still sees it plainly, and almost in the same direction that it was at the beginning, he knows that the light, whatever it may be, is miles away from the line of the road. Give him the proper instruments, and the time and skill to use them, and let him take an observation. at each of the mile-posts, and he can tell just how far away the light is which he is watching.

This is the way in which the civil engineer measures his way along from point to point across a continent. This is the way in which the astronomer essays to fathom the depths of space. The Earth is his train. He notes, with his instruments, the exact direction of a star, and six months thereafter looks at the star again. The Earth, meanwhile, has made half its annual revolution, and is now one hundred and eighty-five millions of miles from its former place. This immense distance becomes the base line of his triangulation. And yet, of the myriads of stars visible in these United States, all but about a dozen, when observed with the utmost accuracy, and with the aid of the best telescopes that modern skill can produce, seem not to have changed their apparent direction a hair's breadth.

Part third describes the Solar System, the little family of worlds, numbering two hundred, and probably more, to which our earth belongs. In this comparatively narrow field scientists have found problems which tax their powers to the uttermost, and some of which are still unsolved. In fact, so many of the older statements have been found clearly incorrect, so many things found doubtful which were once considered settled, so many new questions come up which as yet have found no answer, that the astronomical publications of even twenty-five years ago need corrections and additions on almost every page.

THE SUN. In regard to the central body of our system modern investigations disprove much and explain little, and the In the mysteries of this burning mass are denser than ever. ages before the invention of the telescope the highest science The idea claimed little beyond what any untaught eye can see. naturally occurring to the mind of an inquirer was that the Sun is an immense orb in a state of intense ignition, perhaps molten;

and that what wesee is the dazzling surface of this fiery ocean. But the telescope reveals spots darker than the surround

ing spaces, and sometimes many thousand miles in diameter. Figure 67 shows how a spot may be traced from day to day, as it traverses the disk of the Sun from east to west, its changes revealing the fact that it is a real depression in the luminous surface. These spots were at first conjectured to be scoria, masses of dross, floating on the burning sea. But closer observation showed that they have a dark center, and lighter borders, and as the Sun revolves assume the different aspects of vast excavations.

To explain these facts the theory was adopted by Herschel and others, that the body of the Sun is invisible, and that the light and heat come from a luminous atmosphere, the spots being temporary openings in this atmosphere, disclosing the darker surface of the Sun itself. And astronomers that were devout as well as scientific have fancied that under this glow

ing canopy of flame, and defended from its fervors by intervening spaces filled with some ethereal fluid that does not permit the intense heat to pass downward, is the home of the redeemed, the city that hath foundations.

Another advance was made, and this dream faded into thin air. It became an axiom in science that no force operates unspent. The Sun evolves every moment enormous amounts of light and heat, which, on all the principles that science teaches, no mere stratum of fiery clouds could send forth from age to age without diminution. Meanwhile instruments and methods continued to improve; the spectroscope began to reveal its wonders, errors were detected, and new phenomena discovered, until, at the present hour, we are justified in saying, in paradoxical language, that we know more about the Sun and know less about it than ever before.

Modern methods treat of the Sun under three heads: the photosphere, the chromosphere, and the corona. The photosphere is the disk of the Sun, visible with or without the telescope. To the unaided eye it seems a round, smooth, shining mass. Seen through one of the larger telescopes the surface presents a mottled aspect, which has been compared to the appearance of rice grains floating in water, or leaves of the willow-tree, interlacing each other in all directions. Traversing this surface, as the Sun revolves, are the spots already described, often enlarging, or diminishing, or even disappearing as they go. What causes them we know not; science may safely multiply conjectures, because proof and disproof are alike hard to discover.

A few years ago the spots were regarded as furnishing the means of ascertaining the time of the Sun's rotation on its axis; but later observations have demonstrated the surprising fact that the regions nearer the poles revolve more rapidly than the equator. Moreover, the equatorial belt does not seem to rotate always in the same period of time, the variation being sometimes twenty-four or even thirty-six hours. For the cause of this there is not even a plausible conjecture. Faye's idea of ascending and descending currents only originates new questions in regard to the nature of the strata, and the cause of the currents. And then there is something in the color of the lighter portion of the spots which is inexplicable. Instead