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SUNLIGHT MYSTERIES. THERE is a chapter of history yet un- fervor, theirs the faith. The harvest of
written. Some day will provide the long tubes and broad lenses was plentiful, hour and the man to tell the story. Then but the efficient laborers in the observathe forgotten name of 0. M. Mitchell will tories were few. be duly honored by American science. Mr. Mitchell lectured on astronomy in Not great in himself, he was the source of many cities and towns, wherever he could greatness in others. What he lacked in get an audience, throughout the country. knowledge he made up in enthusiasm. He was thoroughly in earnest, and thereHe preached a crusade, and his followers fore he interested his hea rs. He told of erected domes on many a hill-top, and what might be seen in the nightly skies, planted telescopes therein. His was the land every man in the audience felt a
wish to become a Newton or a Herschel. ed, and then at once proceed to make new Nothing could be simpler than his pro- discoveries. Strange to say, there are gramme. Get a large telescope (the larger many people yet who have no other nothe better), properly housed and mount- I tion of astronomy.
We have not space here to tell how Mr. I own work. The old is the classic science. Mitchell brought about the building and Its triumphs are won by the aid of mathequipping of an observatory near Cincin-ematics; its labors are the refinement of nati. The first subscribers to the enter- precision. The new study accepts with prise had scarcely any money to spare, thanks all that the elder branch provides, but some of them gave land, others build- but seeks fresh light from a different diing materials, and several assisted in the rection. Either “celestial physics" or manual labor. At last the structure rose, “physical astronomy” is the title by and the telescope was bought on credit. which the young scion is now generally Then certain gentlemen of Cincinnati per- known, but probably our children will mitted the use of their names as trustees. invent a shorter and more convenient They took care, however, to avoid all risk name. Let us frankly admit that we and expense, and to secure free tickets to can not call a man a “physicist” without Mr. Mitchell's lectures. If the story could a muscular effort, and a fear that some be fully told, you would smile at it through unlearned by-stander may think we mean tears. Here is one of the stipulations: a physician. The distinction between the
two kinds of astronomy is well marked. “Art. 8.—It shall be the duty of the astron, One deals with the places and motions of omer to take charge of the observatory, and the heavenly bodies; the other strives to the books, instruments, and apparatus therein, belonging to the society, and preserve them ascertain the materials of sun and stars, as far as possible in complete order. He shall and the effects of their radiations. It is conduct a series of scientific observations such the business of the first to say where as may, in conjunction with other similar ob- things are; of the second to say what servations, conduce to new discoveries and they are. The Allegheny Observatory, perfect those already made in the heavens. under the charge of Professor S. P. LangIt shall further be his duty, by himself or such ley, is one of the younger kind; it is deassistants as he may from time to time appoint, to aid in gratifying the curiosity of such voted to “solar physies.” members of the society as may desire to ex
There are men to whom the question amine the heavens through the telescope. He whether the sun is ninety-two and a half shall also deliver each year a course of lec- or ninety-three million miles from us is tures before such members of the society and of more interest than the opportunity of such other citizens as may purchase a ticket hearing Patti or seeing Langtry, or even to the same; the sale of these tickets to constitute his only compensation for the services Some of these men have recently gone to
than the certainty of three meals a day. rendered to the society, provided that the owner of two or more shares shall be entitled the ends of the earth to observe the transto free admittance to all such lectures."
of Venus. They hope thereby to mea
sure the sun's distance a very little more Similar enterprises, struggling with like accurately. With the best possible luck, difficulties, per aspera ad astra, sprang these experts in the elder branch of asup in the wake of Mr. Mitchell's crusade. tronomy can only have the pleasure of Many of them never reached the altitude helping to solve a mathematical problem. of having a large telescope and a load of The younger science offers a more palpadebt; very few passed that point. Among ble kind of enjoyment. It deals with the latter was one founded in a suburb of light and warmth and color. Its proofs Pittsburgh, Pennsylvania. Fair science appeal to our senses as well as to our reafrowned not on its humble birth. Two son. All of its experiments are delicate; pieces of great good luck came to this ob- some of them are exquisitely beautiful. servatory: a young astronomer of zeal To many of our readers, though not to and ability was made its director; a liber- those who have perused a recent work of al-minded citizen of Pittsburgh became its Dr. C. A. Young, it may be as new as it helper. It has the disadvantage of over- was to the writer to learn that light from looking the smokiest city in America. different parts of the solar disk is of difEven on the hill where the observatory ferent colors. The apparatus by which stands your hands are blackened when this is shown throws two patches of light you open a gate, and you can see little side by side on a screen; they are as unflakes of soot falling slowly through the like in hue as a sapphire and a garnet. sunshine.
One is light from the centre of the sun's Astronomy has differentiated. There disk, and has a decidedly blue tint; the is the old and the new, each having its | other is light from near the edge of the
VOL. LXVII.-No. 397.-6
RAYS THROUGH SOLAR
sun, and has a murky, chocolate color. / questions about solar light and heat, the The difference is due to the fact that rays welfare of civilized man could soon be adfrom any part of the sun near its edge vanced by longer strides than have resultmust pass to us through a much greater ed from the uses of steam and electricity. thickness of the solar atmosphere than We are wholly dependent in many ways rays from the centre. Draw two concen- upon the emanations of the sun for contric circles, the space between them repre- tinued existence. All our food and clothsenting the sun's atmosphere, the inner ing has been made by the absorption of
circle the sun.
We are “souls of fire To a point where and children of the sun." By whatever the observer is path we seek the laws and causes that supposed to be, govern climate, harvests, weather, we outside the cir- shall find their origin at the centre of the cles, and on a solar system. A complete science of the level with their sun would enable us to foresee the years centre, draw two of famine or of plenty as surely as we lines from the now predict the positions of the planets. inner circle, one A perfect. system of weather forecasts
from the top or would take the place of uncertain “probbottom, the other from the middle. It abilities.” The date for the coming of the will be seen at a glance that the line from frost-king, or of the overflows when his top or bottom passes through a greater icy fetters are broken, could be named evspace between the circles than the central ery year far in advance. The navigator line.
might learn before he started on a voyThere is no doubt that the sun has an age what storms he could avoid, or when atmosphere, an envelope of thousands of and where he must prepare for their enmiles in thickness. In respect to the prop-counter. With such objects in view, the erty of cutting off blue rays, and permit-younger science is begging for help and ting red ones to pass, there is a curious recognition. Meanwhile the old estabsimilarity between the atmosphere of the lished astronomy has all the national aid sun and that of the earth. Most of us and nine-tenths of all private endowments. have noticed that sunlight near sunset, In the new researches not only is there when the rays can only come to no royal road, there is not even an opened through a far greater breadth of air than path. The way must be found by careat noon, has a reddish tinge. It has ful observation and measurement. At been generally supposed that the vapor Allegheny experiments have been espeof water in the lower strata of our air cially directed toward finding just how has most influence on the color of the the sun's light and heat are modified by sunset rays. But this can hardly be the intervening atmospheres. In 1878-9 a case with the sun's atmosphere. True, systematic work was begun in measuring an eminent Italian savant has put on exactly the degree of heat in all parts of record some spectroscope observations the solar spectrum. Previous studies of that he regarded as showing traces of wa- this kind had been made by experimenters tery vapor in the envelope of the sun-a who used the spectrum thrown by a prism. locality which we should naturally sup- It was proposed instead to investigate the pose to be drier than the skeletons of a spectrum given by a “diffraction gratmedical museum. Whatever may be the ing. There were good reasons for this explanation, the striking fact remains of choice. A “grating" is a surface of glass this similarity of atmospheres under total- or of speculum metal scratched with parly unlike conditions. Several years ago allel lines by means of a diamond guided Professor Langley made the observations by a ruling machine. The iridescent colon difference of color, and it interested ors of mother-of-pearl, and of the winghim so deeply as to give a permanent di- cases of certain insects, are similarly the rection to his studies. He wished to learn result of numerous lines, close together, more about the sun-rays, and of the ef- which can be seen by the microscope. It fect upon them of absorptions by both at- is said that the play of colors can be transmospheres.
ferred to white sealing - wax by simply If some superior being could and would taking an impression from the motherconfer upon us a revelation answering all of-pearl. The spectroscope gratings that
give the best results are ruled with from which each ray diverges from the straight eighteen thousand to thirty thousand lines line that uninterrupted light would have to the inch. Latterly some great im- taken. That distance, as may be shown provements have been made in this kind by a simple problem in geometry, is proof apparatus by better ruling and by giv- portional to the wave-length of each ray. ing the grating a slight concavity. The Prisms distribute the rays unequally. spectrum is reflected from the ruled sur- In the spectrum produced by flint-glass, face, and can either be thrown on a screen the blue end, containing the rays of short or observed with a telescope. The screen wave-length, is well displayed ; but the is, of course, to be placed at the focal point red end, where are the rays of long wavewhere the concave form of the grating length, presents them crowded together. makes the reflected image brightest. The normal spectrum, on the other hand,
The writer had an opportunity of seeing as given by even the best of gratings, has what could be done with an excellent grat- its inconveniences. It gives several specing on a day of superb sunshine at Alle- tral images instead of one; these partly gheny. To those who have never looked overlap, and have to be separated. In through a spectroscope no description can some parts of it the heat is very faint. give an idea of the purity and beauty of Speaking of heat, an apology is needed. the colors which it reveals, blending them Science sometimes blunders. Until very from tint to tint in an unbroken harmony. recent years text-books have given forth The sharpness of the Fraunhofer lines the notion that there are three distinct was, however, the most interesting feature kinds of rays emanating from the sun-of this occasion. Scarcely more than ten light rays, heat rays, and actinic or chemyears ago the announcement was still made ical rays--and that these occupy different in standard treatises that between the D portions of the spectrum, though overlaplines in the spectrum (which are caused ping in its middle region, leaving one end by the vapor of sodium in the sun) “a bare of beat and light, and the other end fine line appears in a very perfect instru- bare of light and actinic power. This noment.” Soon after it was first seen this tion, with all that it implies, is now disline was identified as one of the many that carded. Dr. Young states the correct view are produced by the vapor of nickel, and as follows: “All the waves of solar radiaits visibility became a test of the good- tion are carriers of energy, and when inness of a spectroscope. The apparatus at tercepted do work, producing heat, or visAllegheny, when the spectrum was thrown ion, or chemical action, according to ciron a screen, showed the two D lines wide cumstances.” It may be convenient to apart, with the nickel line plainly to be speak of heat rays, but it is not accurate. seen between. A small telescope was Actinic power has been found throughout then substituted for the screen. The writ- more and more of the spectrum, by using er again examined the space between the chemicals that are duly sensitive. CapD lines, and though not skilled in such tain W. de W. Abney, of the Royal Engiwork, found without effort two lines, some- neers, is said to be able to photograph a what faint, yet distinctly visible, in the in- tea-kettle at boiling heat by its own radiaterval. Fourteen were counted by an- tions in total darkness; Horace Greeley other observer.
was not mistaken in his use of plain hot The great advantage of the diffraction water as a stimulant drink. The experispectrum over that given by a prism is ments at Allegheny prove that there is that the former presents the rays in an measurable heat in every part of the specorderly manner Without going into ab- trum. As to light, the human eye is limstruse details, it may be briefly stated that ited in its range. The optic nerve does the image obtained from a grating has not respond to rays of very short or very been properly called the normal spectrum, long wave-length. Hence we do not see because the rays in itare dispersed equally either end of the spectrum. All our senses throughout its extent, and their places in are in like manner limited; for instance, it are proportional to the length of their sound waves of very high or very low waves. Every spectrum is composed of pitch are inaudible. There is strong evirays that have been bent; that is, on leav-dence that certain animals hear sound ing the prism or grating they travel in a waves that are not sounds to us, and that new direction. In the normal spectrum other animals get the sensation of light, there is a certain angular distance by if not of color, from waves of slow vibra