we find that and the rank together in the distribution of light on their surfaces. "Sunlight at is of the intensity that it is at the earth or the moon, and we should expect, with a similar reflecting surface, that would show only about of the chemical intensity of the moon, whereas its central parts almost equal the average surface of full moon. (The intensities are in the ratio of 4 to 5, about). So we must suppose to be either chemically self-luminous, or else that it has a very peculiar property of light, reflection affording X27=22 times actinic intensity of moon-light. This may be possible; its surface presented to us is gaseous, the moon is solid. "The spots, or faculæ, on Jupiter remind us of the sun, and it is curious to notice how the discordances in the sun's rotation from proper motion of spots is paralleled in the case of 2's rotation, which fluctuates between 9h 50m and 9h 56m, a very decided inequality. Then again, the question of the recurrence of spots in the same region is not established, though suspected with both bodies. "The arrangement of sun-spots in zones and their prevalence in low latitudes, accords with Jupiter's belt action. "I have seen 's bright regions mottled like the sun, and com pared the two to each other, years ago. 's spots are sometimes not dusky simply, but black, at any rate so-called, though we must not lay too much stress on an expression adopted perhaps hastily. The transit of Jupiter's satellites as black spots I have often witnessed. These always enter and pass off bright, as seen projected on the margin of the disc. The old explanation, which attributed the appearance to dark spots on the satellites, will not meet the facts, by any means. The first satellite is not black, or even always dark, excepting on a bright zone. "The grand objection to the idea of Jupiter's self-luminosity is the darkness of the shadows cast by the satellites, but it is a question how much defect of light in an object projected on a bright background will cause it to look black, especially when it subtends only a very small angle. "Perhaps if the side of Jupiter turned away from the sun be bright, we ought to see the satellites in eclipse. Here is another difficulty. Then again SEIDEL makes Jupiter, Venus and Mars have equal "Albedo," which militates against the idea that Jupiter is any more self-luminous than Venus, for instance. I think there must be an error in the monthly notices of the Astronomical Society for January 1860, page 102, as regards the Albedo of Saturn and Mars. The latter is fainter than Saturn, allowing for distance from sun and areas of illuminated surface. "I have been looking into the relation between the period of sunspots and the position of the principal planets as, in case of extensive chemical action going on in their atmospheres a reflex action on the sun, a sympathy between them, might be anticipated. At first all was promising up to 1826, as Jupiter's perihelia and aphelia answer tolerably to maxima and minima of spots, but previous to 1826 there is too much divergence. * * * "At all events, Jupiter should be studied henceforth with special reference to the relation between the physical constitution of its atmosphere and that of the sun." GRANT TO THE LICK OBSERVATORY FROM THE SMITHSONIAN INSTITUTION. The Smithsonian Institution, through its Director, Professor LANGLEY, has granted to the Lick Observatory a sum of money sufficient to provide a portion of the apparatus to be used in making enlargements of the Moon with the photographic object-glass of 33-inches aperture.. Experiments in this direction are already in progress. E. S. H. HARVARD COLLEGE OBSERVATORY EXPEDITION ΤΟ SOUTHERN HEMISPHERE. THE The following paragraphs from the New York Herald give one of the best accounts of this expedition which has so far appeared in print: "The Harvard Observatory's expedition to Peru is on the eve of setting out-probably the best equipped, as it is to be the most comprehensive, scientific expedition ever sent forth. "In prosecuting its self-assumed task of making a complete map of the heavens, the observatory has found it necessary to establish branch stations in order that the entire sky may be mapped, and, for this purpose, an astronomical plant has for some time been in operation on Wilson's Peak in Southern California. In May, 1889, a similar station was erected at Chosica, Peru, and there S. I. BAILEY and M. H. BAILEY, two of Professor PICKERING'S lieutenants, have been at work systematically observing the southern hemisphere of The observers at Cambridge have done all that they can do. in this line—that is, they have located and described all the stars which stars. they can see. The observers at Wilson's Peak have collaborated to the best of their ability, and so have those at Chosica. "In the latter case, however, climatic conditions have interfered to a very considerable extent, and it has been found necessary to remove the observatory to a point where the cloudy season is at a minimum. Mr. BAILEY made a temporary location in the desert of Atacama, one of the dryest spots of the earth and nearer the coast than Chosica, and it has been concluded to establish a permanent observatory at a point near the city of Arequipa, where an eligible. position has been secured at an altitude of about 8000 feet. To this point Professor W. H. PICKERING, accompanied by his family and by Messrs. A. E. DOUGLAS and R. W. VICKARS as assistants, is about to start. The BAILEY brothers will return to Cambridge after the new observatory shall have been established, but the party, which now goes, does not expect to see North America again in six or eight years. By the end of that time Professor PICKERING expects to have mapped the entire southern half of the heavens, which, as is well known, is far richer in bright stars, clusters and nebulæ than the half with which we are familiar. He also will have hitherto unequaled opportunities. for observing comets. "Professor PICKERING also expects to be able to secure photographs of the moon which will be superior to any yet made, and he promises to show me at a date not very far distant a picture of her lunar majesty six feet in diameter. One of the results of the expedition, which will be of the greatest interest, will be the observations of Mars, which will be made when the mysterious little planet approaches the earth in August, 1892. Mars will then be nearer the earth than since 1872, and far to the south, and this fact, together with Professor PICKERING'S altitude and the superb instruments at his command, leads to the expectation that we may be on the eve of remarkable discoveries regarding our very interesting planetary neighbor. "The location selected is the easiest in the world to reach, for a line of railway leads to it from the coast, and thus the delicate and heavy instruments can be transported with ease and safety to the desired altitude. There are now in Peru, belonging to Harvard University, an 8-inch photographic doublet, a 5-inch visual telescope and an instrument for measuring the brightness of stars. Professor PICKERING is to take with him his unequaled "battery," a 13-inch photographic telescope, with an 8-inch "finder"; a 20-inch reflector, made in England, for photographing faint nebulæ; a 21⁄2-inch camera, mounted equatorially, the instrument which discovered the great spiral in Orion; a portable transit for determining time, and a seisometer for observing earthquakes. Next year a 12-inch visual telescope will be added to this phenomenal equipment, so that there can be no failure on the ground of lack of instruments. "There is no wood in the country where the expedition is going, and therefore, a great many things not at all astronomical-a dwellinghouse, for example-have to be taken along. The steamer which takes the party will have in her hold even the domes and the iron piers for the telescopes. "The observatory at Wilson's Peak has been temporarily abandoned." SPECTROSCOPIC INVESTIGATIONS AT THE JOHNS HOPKINS UNIVERSITY [BY PROFESSOR H. A. ROWLAND]. "The visible and ultra violet solar spectrum has been compared with the spectra of different metals and the position of the metallic lines marked on the spectrum map with the view to identifying as many as possible of the more important lines of the solar spectrum. In this way the spectra of all known metals, with one or two exceptions, have been photographed and compared with that of the sun and its presence or absence in the sun determined. Silicon has thus been found in the sun for the first time. Many important solar lines have also been found to be due to vanadium and scandium. The presence of silver has also been definitely determined. Photographic studies have also been made of the spectra of various chemical preparations of minerals containing rare earths, with the view of isolating the spectra of the various components. This research is yet very incomplete. "The homologous lines in the spectra of zinc and cadmium have been carefully compared. The so-called " 'second spectrum of hydrogen' has been photographed in connection with the sun, and the wave lengths determined, and the spectrum of nitrogen has been photographed and studied in the same way. The various formulæ for the arrangement of lines in band spectra have been tested by means of more accurately determined wave lengths. Investigations have also been made of the effect of heat in modifying the magnetism of iron bars, of the cause of the enormous apparent values of the specific inductive capacity of amyl alcohol and certain other imperfectly insulating liquids. A large number of diffraction gratings have been ruled on the dividing engines for the use of investigators throughout the world. A series of photographic spectra of the metals from wave length 2000 to w. 1. 6000 has been obtained, and eye observations made on many of them to the limit of the red rays. These are in conjunction with the solar spectrum, and the original negatives are on about the scale of ANGSTRÖM's map. The negatives are each nineteen inches long. A micrometer has been constructed measuring wave lengths direct to 5000 part. "During the year there have been eighty-one students in the department of Physics, twenty of whom were graduates." -From the Annual Report of the President of the RECENT IMPORTANT PUBLICATIONS. Miss AGNES M. CLERKE: The System of the Stars; pp. 424, six plates and many wood cuts. Dr. J. L. E. DREYER: TYCHO BRAHE-a picture of scientific life and work in the XVI century; pp. 405, five plates and several cuts. H. H. TURNER and A. A. COMMON: The Companion to the Observatory for 1891. (See Publications A. S. P., vol. II, p. 26). W. T. LYNN: Celestial Motions-a handy book of Astronomy. Sixth edition. ARTHUR COTTAM: Charts of the Constellations. (Probably the edition in book-form, 12x15 inches, will be found most generally useful to amateurs). E. W. MAUNDER (Editor): The Journal of the British Astronomical Association (monthly). (Vol. I begins with October, 1890). J. SCHEINER: Die Spectralanalyse der Gestirne; pp. 474, two plates, seventy-four cuts. R. VON KÖVESLIGETHY: Grundzüge einer theoretischen Spektralanalyse; pp. 327, plates. C. E. DUTTON: The Charleston Earthquake of 1886; pp. 185, and many cuts. A HURRICANE IN AN OBSERVATORY AND WHAT IT DID THERE! [Extract from Madras Observations, vol. 4, 1836-37 by T. G. TAYLOR, pp. 2-3.]* "These numbers hold good up to the 30th October, 1836, when the wires were broken-in consequence of the shutters on the roof of the observatory being blown open by the violence of the wind, whereby the instrument was exposed for some minutes to very heavy rain, having failed during this time to secure the shutter. * * * * I was compelled to take the transit off its axis, and * This extract was kindly copied for us by WM. C. WINLOCK, Esq., of the Smithsonian Institution. E. S. H. |