man.

The observations which are made in eclipses of the sun may be divided into two kinds: first, those which refer to the time of the motions of earth and moon; and second, those which refer to the nature of the sunlight. In regard to the former, we remark here that every eclipse of the sun will serve for a correction of the elements of the orbits. The time when the moon enters the disk of the sun, the duration of the eclipse, and the time when the last trace of the moon leaves the edge of the sun, have been calculated beforehand with the utmost minuteness, even for the twentieth part of a second, thanks to the accurate knowledge which our astronomers have of the motions of the earth, and of the infinitely more complicated motions of the moon. Now, if the mentioned phenomena happen exactly at the time calculated, they evidently confirm the correctness of the calculations, and of the supposed motions and distances of these heavenly bodies. But if there is a discrepancy, even of the twentieth part of a second, the previous calculations must be corrected, and thus every new observation will furnish either a new proof of the absolute correctness of the astronomical calculations, or lead to corrections which finally must approximate this part of astronomical knowledge to a state of absolute perfection.

But by far the most important part of the observations which will be made in this eclipse refer to the nature of the sunlight. There is a very widely spread opinion that in a total eclipse of the sun a total darkness prevails, and that the stars become visible. This opinion, though repeated by our astronomical handbooks, is entirely erroneous. Only the very brightest stars become visible. Thus, in the total eclipse of July 18, 1860, the four planets, Mercury, Venus, Jupiter, and Saturn were seen near the sun with the naked eye, and in the total eclipse of July 28th, 1851, in Dantzic, Mercury, Venus, Jupiter, Procyon, Regulus, and Spica were visible; but it was in vain that Galle tried to find Castor and Pollux. The fact that during a total eclipse there is only a twilight, but by no means darkness, is easily explained, when we consider that the atmosphere in places next to the total eclipse will

But there is another phenomenon which, in the moment of the total eclipse, is presented to the eyes of the observers, so glorious and wonderful that no description can give an adequate idea of it. This is the corona, which suddenly appears in the moment when the last ray of the sun disappears behind the deep black cover of the moon: a shining wreath of beams, surrounding the totally eclipsed sun to a distance of about one-third of the apparent diameter of the moon, and so bright at its inner edge that we may doubt whether really the whole sun is obscured, and then fading away imperceptibly in the vast space of heaven. The corona does not always present the same appearance; it is either of a silvery white or of a reddish tinge, according to the state of our atmosphere, and sometimes colored rays or pencils of light are seen issuing from it. The halo with which painters surround the heads of saints gives, perhaps, the best idea of it. It disappears with the first reappearing ray of the sun, as if by magic.

What is the cause of this phenomenon? It must be either in the sun or in the moon. The moon could produce it only if she had an atmosphere capable of refracting the rays of the

sun.

But since it has been proved that the moon is without an atmosphere, it follows that the cause of the phenomenon must be found in the sun itself.

The following theory was adopted by the best astronomers before the discovery of the spectrum analysis:

If we observe the sun through a good telescope, we see black spots on its surface, irregu larly formed, and surrounded with a penumbra, that is, an inner ring, which is less dark, and of an ashy-gray color. These spots often combine into a single larger spot, or separate into different smaller ones, passing over the disk from east to west in periods of nearly two weeks. Sir W. Herschel, and after him most. astronomers, believed these spots to be openings in a luminous atmosphere of the sun, which alone is the cause of the sunlight, and that the sun, whose body these very openings allow us to see, is dark; that this luminous atmosphere (photosphere) is separated from the body of the

sun by an inner atmosphere, tending to intercept or to soften the heat and light of the photosphere, and that the penumbra is produced by this inner atmosphere.

But there are several important objections against this theory. Thus it has been observed that the spots, although moving around the sur. face of the sun nevertheless retain their shapes often for a long time. But by Sporer's investigations it has been proved that the surface of the sun is perpetually agitated by the most violent and tremendous storms, moving near the equator in a westerly, in higher latitudes in an easterly direction. But how can the spots, if mere interruptions of a gaseous atmosphere, retain their shape, when this atmosphere itself is driven over many thousands of miles in the most violent convulsion? Again: several astronomers have observed that both the spots and their penumbras are traversed by streaks and veins of sunlight. W. Carrington, in Redhill, saw on the first of September, 1859, an intense white light, brighter than that on the surface of the sun, suddenly emerging from the center of a large spot. The phenomenon lasted five minutes, and after its disappearance the spot remained unchanged. The same astronomer inspected some days later the photographic magnetic records in Kew, in respect to declination, inclination, and intensity, and found in each of these the traces of a vast disturbance, which had occurred exactly at the time of the phenomenon described above. In 1862, the astronomer Nasmyth stated that he had observed in the penumbra of the solar spots, things looking like willow leaves, which placed themselves over each other like bridges over bridges. In 1863 other astronomers observed the willow leaves of Nasmyth, and ventured to assert especially Sir John Herschelthat they might be living beings, developing light and electricity. Even the earth was affected by this phenomenon, for at all observatories magnetic storms were observed, all telegraph wires were overloaded, and an aurora borealis trembled on the sky.

It is evident that the hypothesis which we have stated in regard to the solar spots is unable to explain any of these phenomena. Much less can the appearance of the corona be explained by it. In order to account for the corona astronomers have resorted to a new hypothesis; the existence of a third atmosphere around the sun-a cloudy sphere. This sphere, they say, is invisible under ordinary circumstances, in consequence of the brighter photosphere; but during a total eclipse it will appear as corona, either with its own light or by reflecting the rays of the photosphere.

But the corona is not the only, nor even the most remarkable phenomenon of a solar eclipse. For at the moment when the last ray of light has vanished, we suddenly behold on the edge of the dark moon strange conglomerations of a pale reddish lustre, which some observers have compared to glaciers, illuminated by the rising or setting sun, others to reddish mountain peaks, others to immovable flames. These protuberances-so they are called-are not always connected with the edge of the moon or the sun, but often are separated from it by a consider able distance (up to two and a half minutes.) Some, when the moon is about to glide over them, suddenly change their colors, or seem to grow in height, and then new protuberances will make their appearance. These protuberances have especially been seen near those places on the edge, where solar spots have been perceived before the obscuration.

These protuberances were several times observed during the last century, first in 1733 by Bassemius in Gothenburg. But they did not engage the attention which they deserved till Schumacher made his admirable observations in Vienna on the eighth of July, 1842; since that time they have been observed by all astronomers with the most minute care during all total eclipses-in 1850 in Honolulu, 1851 in Sweden and Prussia, 1858 in Peru and Brazil, 1860 in Spain. It is for the sake of getting photographic likenesses of the protuberances and the corona that numerous astronomers who have resorted to the scene of the present eclipse have provided themselves with photographic instruments, which, by the skill of Warren de la Rue and Secchi, produced surprising results at the occasion of the last eclipse.

Some astronomers think that the protuberances bear the same relation to the outer or cloudy atmosphere of the sun, as the terrestrial clouds do to our atmosphere. Others consider them as volcanic masses, formed in or below the photosphere, which have penetrated through the openings that appear as solar spots, and perhaps have caused these openings. Others suppose them to be optical phenomena produced by the refraction of light. Some have even considered them as real mountains, which, however, according to their apparent size, would have a height of about two hundred miles, if they were on the moon, and of about sixty thousand miles if on the sun.

All these problems have entered a new phase since Bunsen and Kirchhoff, ten years ago, discovered the analysis of the spectrum. We will endeavor to give the reader a brief outline of this splendid discovery, one of the most im

portant of this century, and especially designed to revolutionize the science of chemistry.

Newton discovered that if a beam of solar light be admitted to a dark room through a small aperture, and intercepted by a triangular glass prism, the rays of the sun will be dispersed into an oblong, colored figure, which-especially when observed through a telescope looks like a piece cut from a rainbow, with the known succession of the seven colors, viz., red, orange, yellow, green, blue, indigo, violet. This figure is called the prismatic solar spectrum. The spectra of the planets, but not those of the fixed stars, show exactly the same succession of colors. In the year 1814 Frauenhofer found that the colors of the solar spectrum are not exactly contiguous, but separated by a number of black parallel lines, which are vertical to the length of the spectrum. These lines, whose number is now known to be nearly two thousand, always appear exactly at the same places of the spectrum, however much the angle of the prism may be altered, so that we may consider them as the regular borders of the several groups and shades of colors.

Scientists were in the dark concerning the origin and nature of these lines, until recent peculiar discoveries shed an unexpected light on the subject. These discoveries were made by comparing spectra not having their origin in the sunlight. Thus it was found that in the spectrum of chloride of sodium (common salt) the colors appear much darkened, with a very bright yellow line at the place where the red color changes into orange. This yellow line is a characteristic proof of the presence of sodium in any body in a state of combustion. Electric light does not show any dark lines in the spectrum at all. But if a flame of alcohol, the wick being saturated with sodium, is interposed between the prism and the electric light, a dark line will appear in the place of the bright yellow line. Now Bunsen and Kirchoff discovered that the mentioned dark line exactly coincides with one of the lines of Frauenhofer in the solar spectrum, and that the same phenomenon is repeated in innumerable other cases. To each chemical element, treated in this way, corresponds a dark line, or a series of dark lines; and if several elements are combined, the corresponding dark lines appear separated without the slightest confusion.

By this discovery an entirely new way of chemical analysis was found. By means of the spectrum may be recognized the presence of the very minutest particles of elements in terrestrial bodies, particles so minute that by no other method can even a remote approximation to this delicacy be obtained. Thus, the spec

trum analysis has disclosed the presence of one trillionth of a pound of sodium by means of the characteristic yellow line in the spectrum. We may imagine how enormous will be the result of Bunsen and Kirchhoff's discovery in chemical science. But it is hardly of less importance in astronomy. For the same scholars also made the discovery that there is an essential difference between the spectra of solid and liquid and those of gaseous bodies. Solid or liquid bodies brought to a state of white heat produce a continuous spectrum, in which all the colors are contained without the interposition of dark lines. But gaseous bodies produce bright lines interrupted by dark intervals. Now, when the flame of a gaseous body is interposed between the prism and a white hot solid or liquid body, the spectrum of the latter at once receives the dark lines of Frauenhofer exactly at the places where the spectrum of the gaseous body has shown the bright lines, while the dark intervals of the latter coincide with the colors of the spectrum.

The inferences which may be made from these facts are palpable. For it evidently follows that the sun must be a white hot solid or liquid body, surrounded by a gaseous atmosphere, in which a number of elements, some of which are also found on our earth, are in a state of combustion. The body of the sun without this atmosphere would produce a spectrum without black lines. But since we see in the solar spectrum a number of black lines corresponding to the spectra of certain terrestrial bodies, as iron, chromium, nickel, zinc, etc., it follows that these bodies must be present on the surface of the sun, and must be in a state of combustion in his atmosphere. On the other hand, some terrestrial elements, as gold, silver, quicksilver, etc., can not be present on the surface of the sun, since the lines formed by their spectra are not formed in the spectrum of the sun. Many experiments have also been made, consisting of the artificial production of new lines in the solar spectrum. Thus, for instance, we find in the spectrum of lithium a peculiar red line. If we interpose a lithium flame between a sunbeam and a prism, a dark line will appear on the same place where before the red lithium line was found, and which did not exist before in the spectrum of the sun. We infer from this that lithium is not contained in the surface of the sun.

We may now explain the solar spots, the protuberances, and the corona. The solar spots are most probably identical with the protuberances, and both are nothing but clouds, swimming in the atmosphere of the sun, similar to our clouds, which so often appear on the dis

tant horizon, as fantastic formations, like the protuberances. The corona is nothing but this very atmosphere of the sun, of which, under ordinary circumstances, we can not see anything, since its light is too weak to be perceived next to the intense light of the sun.

hands-had placed particles of them in the alembics of our laboratories. American Ed. Monthly.

EXCELLENT ADVICE.-Dr. Samuel Johnson was much attached to a young man, an intelligent Italian. As the Doctor lay upon the couch from which he never rose up, he called his young friend to him, and tenderly and solemnly said: "There is no one who has shown me more attention than you have done; and it is now right that you should claim some attention from me. You are a young man, and are to struggle through life; you are in a profession that I dare say you will exercise with great fidelity and innocence; but let me ex

Perhaps some light may also be shed on the problem of the so-called invisible colors of the spectrum. For, once knowing that the solar spectrum is composed of two elements, which it has hitherto been possible to observe only in their combination, we can not tell what results may be in store for us if we are once permitted to contemplate the one of these elements separated from the other.

We have spoken here only of the importance of the spectrum analysis in regard to a more accurate knowledge of the sun. But we may remark that the spectrum analysis is just beginning to enlarge our knowledge of the other stars in an entirely unexpected manner. Thus, we know that in nearly all stars several of the elements of the sun must be present, as, for instance, iron, sodium, magnesium, hydrogen. But there appears also a difference. Thus, in the brightest star of Orion no hydrogen exists, while in Aldebaran the presence of quicksilver is certain, which is wanting in the sun. In the spectrum of Sirius lines have been found which can not be produced by any known terrestrial body. We know, at the same time, by the most recent discoveries, that the planetary nebulæ can not be clusters of stars, as Sir John Herschel thought to have proved by Rosse's large reflecting telescope, but immense masses of gas without a nucleus; for their spectra do not show dark lines on a bright ground, but bright lines with dark intervals.

What progress of science! How long ago is it that we learned to measure the heavenly bodies? Scarcely a quarter of a century have we known how to find their distances, and not much longer that we have known how to weigh them, as though we could place them in a scale. Now we discover the matter of which they are made—the metals which lie on their surface. We decompose them as if we held them in our

MENTAL AND MANUAL LABOR.-Professor Houghton, of Trinity College, has published some curious chemical computations respecting the relative amounts of physical exhaustion induced by manual and mental labor. Accord ing to these chemical estimates, two hours of severe mental study abstracts from the human system as much vital strength as is taken from it by an entire day of mere hand-work. This fact, which seems to rest upon strictly scientific laws, shows that the men who do brain-work should be careful, first, not to overtask the system by continuous exertion; and, secondly, that they should not omit to take physical exercise on a part of each day sufficient to restore the equilibrium between the nervous and mus. cular systems.-Medical and Surgical Reporter.

WHEN I walk in the woods, I am reminded that a wise purveyor has been there before me; my most delicate experience is typified there. I am struck with the pleasing friendships and unanimities of nature, as when the lichens on the trees take the form of their leaves. In the most stupendous scenes you will see delicate and fragile features, as slight wreaths of vapor, dew-lines, feathery sprays, which suggest a high refinement, a noble blood and breeding, as it were. It is not hard to account for elves and fairies; they represent this light grace, this etherial gentility. Bring a spray from the wood or a crystal from the brook, and place it on your mantel, and your household ornaments will seem plebeian beside its nobler fashion and bearing. It will wave superior there, as if used to a more refined and polished circle. It has a salute and a response to all your enthusi asm and heroism.

Thoreau.

We take pleasure in announcing the name of Mr. J. S. Walthour, of Greensburg, Westmoreland County, as lecturer and instructor before Institutes during the coming season. A successful experience of twenty years as teacher, and three years as County Superintendent, render him amply qualified for the work in which, at the solicitation of numerous friends, he proposes to engage for the ensuing few months.

WHOLE NO. 207.

Associate, J. P. MCCASKEY

upon the Legislature the propriety of voting a fair salary to the State Superintendent. In the last respect Pennsylvania is but little ahead of Ohio, where, as we learned a few days since in Columbus, the State Superintendent of Railroads and Telegraphs is paid four thousand dollars, while but two thousand is the salary of the head of the School Department!

THE ASSOCIATIONS.

At the annual meeting of the County, City, and Borough Superintendents, held in Harrisburg, July 20,-and for the accompanying report of whose proceedings we are indebted to Messrs S. G. Boyd and G. L. Maris, Secretaries—there were present sixty-four of the seventy-six Superintendents now at work in Pennsylvania. Disscussions were had on the subjects of school visitation, the character of exercises proper at institute meetings, the issue of certificates to teachers, the election and duties of school directors, and other matters of practical interest, as previously announced in the circular letter of the State Superintendent calling the convention. Resolutions were adopted recommending a change in the school law, so as to make school directors sworn officers, and allow them compensation for official duty not exceeding one day in each month; asking the repeal of the recent law exempting mortgages, judgments, etc., from taxation for school purposes, said law being found detrimental to the interests of the common schools; recommending an increase of the minimum school term to six months; and the passage of an act requiring county commissioners to provide at the county seat, or such other place as they may designate, a suitable office for the County Superintendent; and urging

National was, like that at the State convention, large beyond precedent.

At Greensburg the attendance of teachers and friends of education was nearly six hundred-more than double the number enrolled at any previous meeting, and enough to test to the utmost degree, the hotel accommodations and private hospitality of this pleasant little town. But it stood the strain nobly, and although an adjourned court was in session, bringing many strangers to the place during the week, still room was found for yet "six hundred." The Deputy Superintendent, as Chairman of the Executive Committee, marshalled the forces for this grand charge. But when Houck's brigade again bears down upon the point of attack, we trust the captured town may be a trifle larger, so as to afford ample accommodations, not only for the camp equipage of field or line officer, but also room for knapsack and blanket of the private in the ranks.

As to the work done during these three hot days of midsummer, the reader is referred to the report of proceedings which occupies a large part of the present issue. Less of practical result may have been attained than was anticipated and desired; and, granting this to be the case, still enthusiasm in our work is aroused anew by such educational mass meetings, which, after all, is one of the chief results of value