Part 10

Line officers are the commanders, navigators, gunners, and, by recent law, the engineers of our ships of war. Marine officers have charge of the policing of ships and shore-stations and of the guns of light calibre afloat. The duties of the remaining officers are indicated by their titles. The titles of line officers and their relative rank, as compared with that of officers of the army, are:—

NAVY. ARMY.

Admiral General. Rear-Admiral Major or Brigadier-General. Captain Colonel. Commander Lieutenant-Colonel. Lieutenant-Commander Major. Lieutenant Captain. Lieutenant Junior Grade First Lieutenant. Ensign Second Lieutenant.

Line and marine officers and naval constructors are educated at the United States Naval Academy; all other officers are appointed from civil life. The Academy was founded in 1845 and is located at Annapolis, Md. The course comprises four years at the school and two years at sea on a naval vessel. The number of cadets at Annapolis is usually about 260.

It is by reason of wars that navies exist, and a few words as to our—now happily ended—conflict with Spain, may fitly close this review of naval progress. The military lessons of that struggle have been fully set forth by able writers. More important, by far, than these is its teaching as regard to our state and future as a nation. The world has learned that the people of these United States are stirred still by the same stern and dauntless spirit which, in Revolution and Civil War, has made and kept us a nation. Furthermore, with one swift stroke, the bounds which in theory and in territory circumscribed us have been swept away, and the United States have passed from a continental to a world power. This is not chance. It is but the leading onward to a destiny whose splendor we may not measure now, whose light and peace and prosperity shall traverse a hemisphere. The one note of sadness in it all is the memory of the gallant dead, of the heroes who fell that this might be. To them, in Cuba and the Philippines, Columbia—with a smile of pride and a sob of pain—drinks in the wine of tears to-day, as the smoke of battle fades.

ASTRONOMY DURING THE CENTURY

BY SELDEN J. COFFIN, A.M.,

_Professor of Astronomy, Lafayette College, Easton, Pa._

ITS PROGRESS, ACHIEVEMENTS, AND NOTABLE RESULTS

Astronomy, the oldest of all the family of sciences, is not a whit behind its sister branches in activity of research and brilliance of discovery. The assiduity and zeal of its devotees are marvelous. The celestial field is so wide, the depths of space between the stars so vast, that no assurance can ever be given to an astronomer that a lifetime of faithful and intelligent research will be rewarded with even a single discovery of importance. In this respect it differs materially from other branches of science.

Nevertheless the patient labor of those who serve in its temple has rarely failed to receive an adequate reward. The discovery made in August, 1877, by Professor Asaph Hall, of Washington, that the planet Mars is attended by two satellites, is a convincing illustration of this peculiarity of the pursuit of astronomy as a study. An indefatigable watcher of the skies for many years, Professor Hall, looking at this planet at its opposition in 1877, when it was unusually near to the earth, was surprised to note two tiny points of light quite close to it; seeing them again the next evening, changed in their positions relative to Mars, it flashed upon him that the firm tradition that Mars had no moons was now disproved. His name will be forever associated with these two bodies, Deimos and Phobos, as their discoverer, although they are but wee orbs, only seven miles in diameter.

I. ASTRONOMY A CENTURY AGO.

The end of the eighteenth century found the Copernican theory of astronomy well established, the principles laid down by Kepler and Newton fully elaborated, and the application of the higher mathematics to the needs of astronomy complete. But there were, as yet, no large telescopes, and observatories were few. In Germany, a great disposition to make observations in this science and in meteorology was displayed in 1783 and for a few years following, and the records then made have proved of much value in confirming discoveries announced at later periods.

When Sir William Herschel, on March 13, 1781, pointed out a little star in the constellation of the Twins, and found that it had a perceptible disk and a slight motion, and was therefore not a star, but a newly found planet, to which the name Uranus was soon given, a careful inspection of the notebooks of previous observers showed that Uranus had been observed and recorded as a fixed star on twenty previous occasions in that century. One man had seen it twelve times, and made his record of it on a paper bag purchased at a perfumer’s. Had he been a man of sufficient order and method to have penned what he saw on the regular records of his observatory, to him would have come the glory of the great discovery of that century.

II. HOW “BODE’S LAW” PROMOTED RESEARCH.

An erroneous guess, if it is a good guess, sometimes produces excellent results. In 1778, Bode, of Berlin, published a “law” that states the distances of the various planets from the sun. It is often expressed simply in this way: Set down 4, and add to it successively the numbers 3, 6, 12, 24, etc., and the sums obtained, viz., 4, 7, 10, 16, 28, etc., represent the relative distances of all the planets from the sun, viz., Mercury 4, Venus 7, Earth 10, Mars 16, [Asteroids 28], Jupiter 52, etc. In reference to all the planets then known to exist, the correspondence of the alleged law to the facts was remarkable. The one point in which the alleged system utterly failed was in requiring the existence of a planet to fill the gap between Mars and Jupiter. So boldly did Biela press his convictions of the correctness of this law upon the notice of his fellow-workers, that they resolved, in 1800, to divide the zodiac into twenty-four zones, to be apportioned among them, for the express purpose of searching for undiscovered planets. This well-organized effort was, erelong, rewarded by the surprising discovery of four new planets, the first one on the first night of the new century, January 1, 1801, and three more soon after. As no more seemed to be forthcoming, the search was relinquished in 1816. A fifth was found in 1845, and nearly five hundred since. Since 1891 photography has been wondrously serviceable in finding these bodies. A sensitive plate, on being exposed toward that part of the sky which it is desired to examine, will record all the perceptible stars as round disks; while any planets that appear in the field of view will, by their motion, leave their trace in the form of elongated trails or streaks, thus betraying themselves at once on the photographs. In this way Charlois, of Nice, Italy, has found nearly ninety small planets. All these planetoids, as the minor planets are often termed, are quite small, being but twenty to one hundred miles in diameter, and not consequential members of the solar system. Bode’s law thus fulfilled its temporary mission; but egregiously failed when Neptune claimed admission to a place in the solar system, for its distance from the sun was utterly out of harmony with that required by the law of Bode.

III. HOW NEPTUNE WAS FOUND.

The patience of Job had a strong parallel in the labors of those tireless toilers to whose minute computations we owe our knowledge of Neptune’s path in the skies. For this far-off planet was discovered not by the use of a telescope, or any optical instrument, but simply by a process of mathematical reasoning. The story is simply this. For sixty years after Uranus was recognized, there were irregularities in its motion that could not be satisfactorily accounted for. In the orbit that it was believed to pursue, it was sometimes in advance of its proper position, and sometimes it seemed to fall behind. Sometimes it appeared to be drawn a little to the right, and at other times as far the other way.

The thought at last came separately to several penetrating minds, not that the observations of its position were in error, but that Uranus must be drawn away from its supposed path by the attraction exercised upon it by some unseen body. And if such an object existed, was it a planet? Where was it? How large was it? What was its path in the far-off ether?

[Illustration: THE MOVEMENT OF URANUS AND NEPTUNE.

The inner circle shows the position of Uranus at various dates; the outer circle the position of Neptune. The arrows show the direction toward which Uranus was drawn.]

In the year 1842, the Royal Society of Sciences of Göttingen proposed as a prize question the full discussion of the theory of the motions of Uranus. It was specially sought to learn the cause of the large and increasing error of Bouvard’s Tables that had been relied upon to show its motion and its precise position at any time. Several able mathematicians undertook this intricate problem. Among them were John C. Adams, of Cambridge University, England, Sears C. Walker, of Washington, a man whose sad fate it was to pass away ere his magnificent abilities could receive extended recognition, and M. Le Verrier, of Paris. Working unknown to each other, they reached similar conclusions almost at the same time. Though not the first to solve the problem, the brilliant Frenchman was the first to announce his result, which he did by writing a letter to Dr. Galle, of the Berlin Observatory, where there was one of the largest telescopes in Europe, and asking him to search for his computed planet, and assigning its supposed place in the heavens. The very night he received the letter Dr. Galle found the planet within one degree of the point designated. The next night it had moved one minute of space, and was also seen to have a perceptible disk. This settled the question, and stamped it as a planet. Le Verrier well merited the title bestowed upon him, “First astronomer of the age.”

IV. METEORITES.

The nineteenth century will be forever memorable for its witnessing the closing career and final destruction of a famous comet. First noticed in France, in 1772, and rediscovered, in 1826, by an Austrian officer named Biela, it bears his name. His computation showed that it traversed its orbit in six and one half years. When it reappeared in 1846, and again in 1852, it was seen to have split into two unequal fragments. It has not been seen since; but at every time when its return should have taken place the earth has passed through showers of meteors supposed to be its constituent particles, and to indicate its entire disintegration.

During the meteoric shower of 1885, on the 27th of November, a large iron meteorite fell in Mazapil, Mexico, and chemical and physical investigation joined to pronounce it a part of the lost Biela’s comet.

The large cabinets of the world contain hundreds of specimens of meteorites, known to be such by their chemical composition, but only a few have actually been seen to fall. The most remarkable fall ever witnessed was that of May 10, 1879, in Iowa, in which the heaviest stone weighed 437 pounds. On April 8, 1893, an aerolite fell near Osawatomie, Kansas, and struck the monument to John Brown that had been erected through the efforts of Horace Greeley in 1863. The meteor broke off the left arm of the statue. A Texas meteorite, owned by Yale University, weighs 1635 pounds. A meteorite that fell in Jiminez, in 1892, now deposited in the city of Mexico, weighs twenty tons; and one lying on the coast of Labrador, which it is proposed to bring to the United States, is said to be still more massive.

V. DO METEORS OFTEN STRIKE THE EARTH?

It must not be thought that meteors usually strike the earth. In truth, but few of them do. The earth is surrounded by them, cold, dark, invisible, because unillumined. It is only when they become heated by rapidly impinging on the atmosphere that they can be seen at all; and unless they come near enough to become subject to the dominant power of the earth’s attraction, they pass off into space unnoticed, and their presence unsuspected.

[Illustration: JAMES H. COFFIN,

Late Professor of Astronomy, Lafayette College, Easton, Pa.]

A case in point is the brilliant “fire-ball” of July 20, 1860, that moved rapidly over the United States, from Wisconsin to Cape Cod, and then passed off into the skies. The entire time of its visible flight over a path of thirteen hundred miles was about two minutes. It was seen about ten o’clock in the evening. It was estimated to be from one hundred to five hundred feet in diameter, allowing for an increase as it expanded by reason of its striking with such velocity the lower and denser layers of the air. Its size and brilliancy were such as to arrest the attention of hundreds of persons, some of whom crouched in fear, and even alleged that they heard it hiss as it flew over their heads. Some fishermen in Lake Huron had ropes over the sides of their boat, ready to spring into the water if it came too near.

James H. Coffin, LL. D., then Professor of Astronomy in Lafayette College, made an exhaustive study of this unusual phenomenon, and, under the patronage of the Smithsonian Institution, published a volume containing many observations that he collected, with the mathematical results derived from them. Professor J. Hann, of Vienna, the highest authority on this subject, said that it was the most comprehensive study of a meteor’s path ever accomplished. Six years were spent in making the computations.

Self-illumined by the heat evolved in striking the various layers of the earth’s atmosphere, it became sufficiently bright to be first seen when seventy miles above the surface of the earth. It was within forty miles of touching us at the time it was over the Hudson River, when the great heat acquired by its rapid transit caused it to burst into two masses, which—like Biela’s comet—continued to pursue separate courses, side by side, until they were lost to view in their ascending flight, being last seen from the deck of a vessel off the island of Nantucket.

No part of the fire-ball struck the earth. Its orbit was an hyperbola, a curve not often found in nature, such that it can never come near us again unless, by the superior attraction of some celestial body, its course may be changed, and a new orbit result.

VI. ASTRONOMICAL OBSERVATORIES.

The Royal Observatory, at Greenwich, England, was founded by Charles the Second in 1675. Its main purpose was to extend astronomical knowledge, so that navigators might better find the position of their ships at sea. This institution retains its prominence. All the longitudes on our maps are reckoned from it, and Greenwich time is used on every ship that traverses the ocean. The “Nautical Almanac,” issued by the Observatory, was an indispensable part of the outfit of every sea captain until, in 1852, the United States provided its own American Ephemeris, a collection of tables of the motions and places of the sun, moon, and planets for every day and hour, and occultations of the stars, with rules for calculating longitude and the like.

Many valuable observations of the transit of Venus in 1769 were made at points near Philadelphia; but almost seventy years ensued before America witnessed the erection of any permanent buildings devoted to the purposes of this science.

President John Quincy Adams, who was highly versed in science, and held the position of president of the American Academy of Arts and Sciences in Boston for twenty years, often urged this matter on the attention of Congress, but without success.

President Thomas Jefferson, who was also a man of no small scientific information, as evidenced in his keeping a systematic weather record at his home in Monticello, Virginia, proposed an elaborate survey of the national coast. This was authorized by Congress in 1807. In the year 1832, in reviving an act for the continuance of the Coast Survey, Congress was careful to append the proviso “that nothing in the act should be construed to authorize the erection or maintenance of a permanent astronomical observatory.”

The expected return of Halley’s comet in 1835 again stimulated popular interest in the science, and aroused an intense desire to provide serviceable instruments, and to establish buildings suitable for their care and use. To Williams College, Massachusetts, belongs the honor of erecting, in 1836, the first astronomical observatory on this continent. Under its revolving dome was mounted an Herschelian telescope of ten feet focus, which later became the property of Lafayette College, where it is still preserved. In 1843, John Quincy Adams laid the corner-stone of the Longworth Observatory in Cincinnati, and delivered a commemorative address, his last great oration. The construction of the United States Naval Observatory at Washington soon followed, and before 1850 there were fourteen observatories established in this country. Nearly all the instruments they contained were made abroad, chiefly in Munich and London. Since then the number has risen to two hundred recognized observatories, of which twenty-four are of superior order, where systematic work is daily pursued, and the results are regularly published in book form. About two hundred observatories exist in other nations.

VII. IMPROVED INSTRUMENTS; THEIR EFFECT ON THE SCIENCE.

The great improvements in telescopes made during the century have been fruitful in two ways; a better knowledge of the surface of the moon and of the planets has been gained, and we have been enabled to learn with precision the exact motions and times of revolution of these bodies and of their accompanying moons. This information, by the use of the laws ascertained by Kepler and La Place, gives us their exact distance, dimensions, and mass. With the increase of telescopic power, the census of the starry host has been so augmented that the number of stars within reach of our modern instruments exceeds 125,000,000. But we had gone little beyond this sort of information until the invention of the spectroscope.

Previous to the year 1859 a few meteors, composed chiefly of stone or iron, some of which had been actually seen to fall from the sky, had been subjected to chemical analysis; but outside of this naught was known of the physical constitution of other worlds than ours. Our ignorance on this point was complete. All our attempts to become better acquainted with the structure of the planets, the composition of the sun, and the nature of the fixed stars would probably have been in vain but for the invention of the spectroscope. This surprising instrument is a master-key with which to unlock many of Nature’s mysteries; her recesses are brought to view, and the farthest star is subjected to an accurate chemical analysis, so far as the light that comes from it is sufficient to disclose the materials of which it is composed.

[Illustration: THE LICK OBSERVATORY, MOUNT HAMILTON, CALIFORNIA.]

The wondrous use of electricity as an agent for the production of light, heat, and power is no greater achievement, in its way, than is Spectrum Analysis in bringing to our earthly laboratories the work of the Divine Hand performed in distant regions of space. Yet the story of the spectroscope is easily told. In its essential elements it is merely this: A ray of light, entering a darkened room through a hole in the window shutter, produces a bright beam on the opposite wall. A triangular glass prism held close to the crevice turns this beam into a band of rainbow hues. If the hole can be changed into a small slit, say one fourth of an inch high and one fiftieth of an inch wide, and if the light can further be made to pass in succession through several prisms, instead of through one, the band will be so elongated thereby that its various and surprising markings can be thoroughly traced and fully studied.

[Illustration: THE SPECTROSCOPE.]

To this band of bright colors Sir Isaac Newton gave the name of the solar spectrum. The image formed by the light of any luminous body, after it has passed through a prism, is said to be the spectrum of that body.

VIII. THE SPECTROSCOPE AND ITS TRIUMPHS.

The spectroscope consists essentially of three tubes joined in the form of the letter Y, one of which is a small telescope, in the focus of which a narrow slit is placed to admit the ray of light that is to be examined; a prism, or a ruled grating that disperses the light, so as to form a spectrum; and a view telescope, with which to observe the various parts of the spectrum.

By using a small telescope to view the spectrum of the sun, Fraunhofer, a German optician, in 1814, discovered that the whole length of the spectrum was crowded with dark lines, very narrow, indeed, but scattered all through the seven hues. He found that sunlight, whether taken directly or reflected from clouds or from the moon or planets, invariably gave the same spectrum; but in no case did light from the stars give a spectrum of the same sort as that from the sun.

[Illustration: YERKES TELESCOPE, UNIVERSITY OF CHICAGO.

Largest in the World.]

Dr. Kirchhoff, of Heidelberg, in 1859, explained the origin of the dark lines, and showed that there are three kinds of spectra: first, that of an incandescent solid or liquid, which is always perfectly continuous, showing neither dark lines nor bright; second, the spectrum of a glowing gas, which consists of bright lines or bands separated by dark spaces. These lines are characteristic of the chemical elements that cause them; and so, from the composition of the bright lines in a spectrum, it is possible to tell their origin. Third, a spectrum crossed by dark lines; which occurs when an incandescent solid is viewed through absorbent vapors.

In the solar eclipse of 1868, M. Janssen first noticed that the solar prominences gave a spectrum of the second kind, and thus proved that the prominences consist of glowing gas. Since that time the march of discovery has been exceedingly rapid.

This simple instrument has thus led the way to a knowledge of the elements composing every heavenly body, no matter what its distance, provided only it is giving out light intense enough to reach our gaze. For the perfection both of the telescope and spectroscope we owe much to the optical skill and mechanical dexterity of the Clarks and Rowland, Hastings and Brashear, all Americans.

About forty chemical elements have now been recognized in the sun. The most prominent are iron, calcium, hydrogen, nickel, and sodium. A distortion, or displacement, of some of the lines in the spectrum enables us to calculate the speed at which the gases are rushing toward or from us. A given line in the spectrum of Aldebaran is displaced toward the violet in such a way as to show that the star is approaching the sun at the rate of thirty miles a second; while a similar line, in the case of Altair, so deviates toward the red end of the spectrum as to prove that it is receding from the solar system at a velocity of twenty-four miles a second. By this principle, recognized by Doppler in 1842, the motions of about one hundred stars toward or from the solar system have been ascertained.