6,260,000 miles, which assuming a parallax of o".2, corresponds to an angular separation of o".014, a quantity inappreciable in even the most powerful telescopes.

Professor VOGEL points out, finally, that traces of the spectrum of the companion can be seen on his plates, in the unsymmetrical appearance of the hydrogen line at a time of maximum motion, and the greater sharpness of other and finer lines at a time of minimum motion, and concludes that the companion, if we could see it, would be of the third magnitude.

Translating the mathematical formulæ of Professor VOGEL into the ideas which they represent, a wonderful picture of stellar motion is presented to our mind, and one to which the whole visible universe, as revealed to us by our greatest telescopes, offers no parallel. The spectacle of two great suns like our own, revolving around each other in only four days, at a distance no greater than that which separates the sixth satellite of Saturn from its primary, is one which the inadequacy of our optical powers will probably ever forbid us from actually beholding, but the indirect evidence that such extraordinary circumstances of motion exist, is so complete that we must admit their reality. If our knowledge of the rings of Saturn rested on evidence of similar character, and not on actual observation with the telescope, the facts to be accepted would seem equally strange. and beyond our experience. The system of a Virginis offers abundant material for speculation. How great, for example, must be the tide-raising forces on the surfaces of such bodies! Actual tides would probably not be found, since it would seem as if the friction of such tides as the forces there acting would produce, would quickly bring the rotation times of both bodies into coincidence with their period of revolution; but both bodies would be distorted far out of a spherical form, and greatly elongated in the line joining their centres. If the distance of the two components were three million instead of six million miles, the bodies probably could not exist as separate masses, but would be torn to fragments by the enormous stresses. This discovery of Professor VOGEL'S, together with similar discoveries by Professor PICKERING, (which are briefly described in Publ. A. S. P. Vol. II, p. 125) opens an entirely new vista in sidereal astronomy, and will lead to wider views of the constitution of the universe.

J. E. K.

ANNOUNCEMENT OF AN ENGLISH TRANSLATION OF DR. DZIOBEK'S TREATISE ON THE MATHEMATICAL THEORIES OF PLANETARY MOTIONS [BY PROFESSOR M. W. HARRINGTON, DIRECTOR OF THE OBSERVATORY OF THE UNIVERSITY OF MICHIGAN].

Dr. DZIOBEK's treatise appeared in the German language in 1888, and has been very well received. Its original publication was aided by a grant from the Prussian Department of Education. It is an interesting fact that an American publisher has been willing to issue, at his private risk, and without guarantees, an English translation of this work, which has been made by Professor HARRINGTON, and revised by the author.

The book is not in any sense an elementary one. Its scope is best indicated by the following extracts from the author's preface:

"The problem of the motion of the heavenly bodies is of great importance in itself, but it is of especial importance to the mathematician. The attempts to solve it, though not entirely successful, have afforded occasion for a display of unsurpassed ability, and have given a great impulse to mathematics. Analytical mechanics, beginning with Newton and receiving its final form from Lagrange, is especially indebted to this problem which afforded it the very foothold necessary for its advance, and though not yet completely solved, it has proved so fertile in suggestion and impulse, that it has determined, to a great degree, not only the direction, but also the rapidity of the advance of mathematics.

Hence, when it is desired to illustrate the abstract theories of analytical mechanics, the profundity of the mathematics of the problem of the motions of the heavenly bodies, its powerful influence on the historical development of this science, and finally the dignity of its object, all point to it as most suitable for this purpose.

"This work is not so much intended for the specialist in astronomy as for the student of mathematics who desires an insight into the creations of his masters in this field. The lack of a textbook which would give, within moderate limits and in a strictly scientific manner, the principles of mathematical astronomy in their present remarkably simple and lucid form, is undoubtedly the reason why so many mathematicians extend their knowledge of our planetary system but little beyond Kepler's laws. The author has endeavored to fill this gap and, at the same time, to produce a book which shall be so near the present state of the science that the latest

investigations shall be included, and even the unsettled questions indicated.

"The subject of the work is that part of celestial mechanics which treats of the motions of the heavenly bodies considered as gravitating points. This is the most important part, and it is fundamental for theories of rotation, of tides, and of the figures of bodies. The author hopes to treat of the latter in a separate work. The simplest processes, and those which best represent the present state of the science, have always been selected and especial care has been taken to guard against the brilliant hypotheses which the explorers of this field have so often indulged in, but which are not suitable for a text-book. The farther advance of the student is aided by the references to the original sources which are invariably given, and which have, almost without exception, been used by the author.

"Farther assistance in this direction is afforded by the sketch of the historical development of the subject which accompanies each important subdivision of the work."

The work is issued by subscription, at a price of $3.50 (orders can be sent directly to Professor HARRINGTON.) It is a matter for congratulation (on several accounts) that the number of orders already received indicates a strong demand for such a treatise in the English language. E. S. H.

BIOGRAPHY OF W. C. BOND.

I

The Boston Traveller is now printing a series of weekly articles. (beginning with its issue of August 2) on the life and works of W. C. BOND, the first Director of the Harvard College Observatory. understand that his granddaughters contemplate the preparation of a memoir of the elder BOND and of his son, Professor GEORGE P. BOND, who was the second Director of the same observatory. E. S. H.

SCIENTIFIC EXPEDITION TO THE SUMMIT OF MOUNT BLANC [BY M. JANSSEN].

M. JANSSEN, Director of the Physical Observatory of Meudon, near Paris, has just made a report of his scientific expedition to the summit of Mount Blanc, which is most interesting in every point of view. The original account is printed in the Comptes Rendus of the Paris Academy of Sciences, vol. CXI, (1890.) The following is a brief abstract. The object of M. JANSSEN's expedition was to determine whether oxygen exists in the solar atmosphere. When the solar spectrum is examined with a spectroscope, at sea level, some lines

are seen which may be due to oxygen in the sun's atmosphere, or which may be due to absorption effects in our own terrestrial air. If the spectrum is examined from terrestrial stations of great elevation, the absorptive effect of the earth's atmosphere is less and less, as the station chosen is higher and higher, naturally. In October, 1888, M. JANSSEN made the ascent of Mount Blanc as far as the GrandsMulets (about 9800 feet above sea), and obtained satisfactory observations; in 1890 he ascended to the very summit of the mountain (15,700 feet), and repeated his work. The immediate scientific result of his two expeditions is that oxygen is not present in the gaseous envelopes which surround the sun; or, at least, if oxygen is present, it is in a condition entirely different from that known to us in our laboratories, and does not produce that absorption of light which is marked by the system of lines and bands familiar to spectroscopists.

This is a scientific conclusion of capital importance in questions of solar physics.

The expedition of M. JANSSEN has an interest quite apart from its purely astronomical one. In fact M. JANSSEN lays the chief stress, in the paper cited, upon the question of the establishment of a high-level observatory at the top of the mountain, and points out the great scientific advantages to be gained from such an observatory, devoted to questions of terrestrial as well as of solar physics. If such an observatory is to be founded anywhere it is tolerably certain. that stations can be found which are far more favorable than Mt. Blanc. Pike's Peak, for example, is 14, 134 feet high, and the summit can now be reached by a railway. There is no reason why a station on Pike's Peak could not be maintained throughout the year, since the U. S. Signal Service kept its observers there for several years continuously. There are also many stations in the Sierra Nevada of California which have natural advantages far above those of Pike's Peak. It would seem, then, that for scientific purposes alone, it might be better to maintain a station at one of these places (to speak only of mountains in North America), than to attempt to found such a station on the summit of Mt. Blanc, which can be reached only with great difficulty and some danger under the most favorable conditions, and which is practically inaccessible during many months of the year. The chief interest in M. JANSSEN's paper, after its astronomical importance, is, for us, the exhibition of his intrepidity in planning such an ascent at all, and of his cool daring in accomplish

ing it. M. JANSSEN is 66 years of age, and suffers from a severe lameness, so that it is practically impossible for him to make continued exertion in walking. During his ascent to the Grands-Mulets in 1888 it was with the greatest difficulty and danger that he attained the cabin at that point, although the ascent is by no means difficult for good walkers. Many ladies, for example, go as far as this. How then was it possible for him to reach the summit, 6000 feet higher, which lies beyond a wilderness of huge rocks and great glaciers with their crevasses, and the route to which runs along steep arêtes only two or three feet wide, with terrific slopes on both sides of the narrow crests? To appreciate the splendid daring of M. JANSSEN, it is necessary to read his own words. It is only possible here to give the merest summary of them.

Before leaving Meudon, M. JANSSEN had a sled constructed which resembled in general pattern the reindeer sledge of the Laplanders. In front and behind this were double parallel cords, united by wooden ungs like ladders. A long line was attached to the front of the sled, and another to the rear. The ascent was made as follows: M. JANSSEN was seated in the sled, and twelve selected guides managed its movements. Two guides, far in advance, sunk an ice-axe in the snow as far as it would go and kept two turns of the forward line wound round its handle. When necessary the other line was kept tight also. The remaining guides pulled on the rope ladders front and back, or, when possible, supported the sled at the sides. In this way, foot by foot, the sled was moved. It was necessary for the guides to cut steps in the steep slopes for their feet to rest in. All that the passenger was required to do was to sit still and keep perfectly cool. This was all-but in the face of the frightful precipices with which the route is surrounded-it was enough.

There are few men whose nerves are steady enough to contemplate dangers of the sort when they are themselves precluded from some sort of physical action. I pass by all the incidents of the route; the passage of the well-known obstacles; the two days and a half spent in a small cabin at the station des Bosses during the prevalence of a hurricane; the ascent of the final slope; and simply recite that the summit was reached during weather exceedingly suited to the observations, and that the descent (which was more dangerous than the ascent) was safely accomplished. The party had been five days on the mountain.

M. JANSSEN says that he is perhaps the only person who has stood on the summit of Mt. Blanc without having made severe exer