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is not improbable, however, that a series of observations of the satellites of Jupiter, throughout its opposition, will be taken with the Equatorial.
An extended discussion of the declinations of 500 principal and miscellaneous stars, with reductions of nearly all published series of declinations to a homogeneous system, is in press. The results have already been incorporated in the American Ephemeris and Nautical Almanac.
Allegheny Observatory, Allegheny, Pa.
Professor S. P. LANGLEY, Director. Replies to inquiries for information in circular of Professor S. F. Baird (without date):
1st. Personnel of the observatory: S. P. Langley, Director; R. F. Hall, Assistant to Director.
2d. Principal instruments: Equatorial, 13 - inch objective, finished by CLARK, 15 feet 3 inches focus, 20-inch hour and declination circles. This instrument has a considerable number of attachments (besides the Filar-position Micrometer) fitting it for physical research. Such are a Prism Spectroscope, of HUGGINS's pattern, and a more powerful one using gratings; a Polarizing Solar Eye-piece, apparatus for projection, etc. An additional lens, 4-inch aperture, of about 150-feet focus (by CLARK), is mounted so that when used in conjunction with the 13-inch objective the so-called actinic rays from the .central parts of the latter may be focussed together for photographic purposes.
An accessory part of the Equatorial, peculiar it is believed to this instrument, has been lately added, consisting of a 12-inch Silvered Plane, by CLARK, mounted at the southern extremity of the polar axis ; so that a fixed solar beam may be sent down the prolongation of this axis by using the ordinary clock-work of the telescope, which, thus considered, becomes a great “Fahrenheit” Heliostat; change wheels in the driving-clock convert it at pleasure into an “August’s ” Heliostat, maintaining a fixed horizontal beam. In either position, heavy apparatus which could not be carried by the Equatorial can be mounted on a firm support and still used in connection with the telescope.
The other instruments are a Transit of the English pattern, 4 inches in aperture; a Chronograph; a Sidereal Clock, by FRODSHAM; a Meantime Clock, by HOWARD; an Accessory Clock, by HOWARD; one Breakcircuit and an ordinary Chronometer, both by FRODSHAM. Besides these, there are a number of minor instruments chiefly adapted to solar physical research.
3d. The principal subjects of observation of the past year have
been connected with solar physics, though studies for the preparation of an apparatus for eliminating personal equation in transit observations have occupied some time.
In solar physics, work is being done here now on the comparison of the heat of the sun with terrestrial sources, on the distribution of radiant energy in the spectrum, and on the change of wave-lengths of light from the different parts of the sun caused by rotation—the latter in connection with an appropriation from the Bache Fundall in active progress. Besides these, other investigations in the same field are in progress.
The routine work for time-determinations has also always been carried on. Besides its work of research, this observatory has been, since 1870, the supplier of time to a large number of railroads, of which it is the official standard, and since to cities. The automatic signals from its mean-time clock have thus been transmitted from Pittsburgh to New York for the past seven years, and during the latter part of that time as far west as Chicago, and over about 6000 miles of main and branch railway lines daily, as well as to the city of Pittsburgh, etc.; and observations and computations for the control of these are made daily.
4th. The work of the coming year, it is anticipated, will be in solar physics very largely, and will, it is hoped, be made to include, for the first time, systematic solar photography. Pending the introduction of this, the usual daily studies of the solar surface will be continued, accompanied (as at present) withi a daily drawing on a scale of 8 inches to the solar diameter, made by projection, and an enlarged drawing of any part of interest, made with the micrometer and polarizing eye-piece. A daily spectroscopic review of the solar limb will be made also, and most of the subjects already mentioned will be continued.
5th. The incompletion of work now in hand, and the desire to make a thorough presentation of it, have limited the publications of the past year.
Three communications to scientific journals, describing results recently obtained here, have been made by the director in the Comptes Rendus des Séances de l'Académie des Sciences for May, 1877, and in The American Journal of Science and Arts for July and August, 1877. Harvard College Observatory, Cambridge, Mass.
Professor E. C. PICKERING, Director. First. The observers and computers at present constantly employed at the observatory building are :
Edward C. Pickering, S.B., Phillips Professor of Astronomy and Director of the Observatory.
William A. Rogers, A.M., Assistant Professor of Astronomy.
Arthur Searle, A.M., Assistant.
Winslow Upton, A.M.; employed in work undertaken in aid of the Coast Survey, and in Equatorial observations.
Miss R. G. Saunders; employed in reductions of the observations made with the Meridian Circle.
Mr. Joseph F. McCormack; employed in assisting in the observations made with the Meridian Circle, and in reducing them.
Mr. C. H. Metcalf; employed in reductions of photometric work.
There are other persons not immediately connected with the observatory who are customarily employed in performing computations for it.
Second. The principal instruments of the observatory are :
The East Equatorial, a refractor of 15 inches aperture and 22} feet focal length, made by MERZ, of Munich, and mounted in 1847.
The West Equatorial, a refractor of 57 inches aperture and 74 feet focal length, made by ALVAN CLARK AND Sons, and mounted in 1869.
The East Transit Circle, made by TROUGHTON AND SIMMs, and mounted in 1848. Aperture of telescope, 41 inches; focal length, 5 feet.
The Meridian Circle.—The object-glasses of the instrument and of its collimators were made by ALVAN CLARK AND Sons; the metal work mainly by TROUGHTON AND SIMMs. The instrument was largely designed by the late director of the observatory, Professor Joseph Winlock, and has done great credit to his ingenuity. The aperture of the principal telescope is 81 inches, and its focal length 9 feet 4.4 inches. The aperture of each collimator is 8 inches, and its focal length the same as that of the chief telescope. The instrument was mounted in 1870.
The Portable Transit Instrument, made by HERBST, of Pulkova, and mounted in 1870. Aperture of telescope, 24 inches; focal length, 33 inches.
Third. The subjects of observation to which attention has been devoted during the past year may be classified with regard to the instruments employed in investigating them.
The work done with the Equatorials has been principally photometric. The objects observed have been the satellites of the superior planets (including those of Mars), some of the asteroids, and some of the fixed stars. Mars and Saturn, and also Jupiter and Venus, have been compared with each other.
Micrometric measures have been made, chiefly of Mars and of its satellites.
The Meridian Circle has been employed, first, in observing the zone 50° to 55° north declination, undertaken by this observatory as its contribution to the work of determining the places of the stars
of the ninth magnitude, or brighter, belonging to the northern hemisphere; secondly, in observing the stars contained in a list drawn up to facilitate astronomical work of various kinds; thirdly, in observing Mars during the period of its opposition, with suitable comparison stars, and also some comparison stars for use by Mr. D. Gill in his observations of asteroids at Ascension Island.
Meteorological observations have been regularly made.
Special observations for clock-error are regularly made, to maintain the accuracy of the clock-signals transmitted to various points in this part of the country, for the purpose of supplying the community with a trustworthy standard of time.
Fourth. The work of the coming year will be a continuation of that just described, with the exception of the observations connected with the recent opposition of Mars. The stars of a list drawn up by the Coast Survey will also be observed at the request of that institution.
Fifth. The eighth volume of the Annals of the observatory was published in November, 1876; the tenth volume in the spring of 1877.
L. Trouvelot's Physical Observatory, Cambridge, Mass. Observer, L. TROUVELOT, occasionally assisted by Geo. H. TROUVELOT.
Principal Instruments.—1st. Equatorial Refractor, by MERZ, 64 inches aperture, 84 feet focal length.
2d. Rutherfurd's Diffraction-plate Spectroscope, by ALVAN CLARK AND Sons.
3d. Apparatus for Photographing the Sun-spots.
The observatory was built early in 1875, and observations begun March 15 of the same year.
During the years 1875, 1876, and 1877, close attention was given to the Sun, Moon, Planets, Clusters, Nebulæ, Double Stars, Meteors, Zodiacal Light, and the Auroral phenomena. From March 15, 1875, to November 30, 1877, the following observations were made: The Sun was observed 955 times, and 48 drawings made. Diagrams made. The Moon“
12 Venus Mars
269 Jupiter's Satellites 35
35 Saturn was observed 136
1 Double Stars
19 Total of observations, 2159; drawings, 571; of diagrams, 121
The Zodiacal Light and the Milky-way have both been particularly studied on every favorable occasion, and elaborate drawings representing them in their most characteristic appearances have been produced.
Besides, a series of thirty-four astronomical drawings in pastel was prepared from the above observations and drawings, and exhibited at Philadelphia at the International Exhibition.
Comparatively few of the results of these observations have yet been published. In 1875 two papers were communicated to the American Academy of Arts and Sciences: 1st. “On Some Physical Observations on the Planet Saturn;" 2d. “On Veiled Solar Spots.” In 1877 three papers were presented to the Academy: 1st. “On the Moon's Zodiacal Light;" 2d.“ Vibrations Observed in the Tail of Coggia's Comet;" 3d. “Sudden Extinction of the Light of a Solar Protuberance."
The series of 127 drawings of Jupiter, made during the year 1876, were forwarded to the.“ Jupiter Committee” of the Royal Astronomical Society in London, and thence sent to Dr. Oswald Lohse, at Potsdam, for discussion, in order to ascertain whether there be any connection between the changes on Jupiter and those on the sun.
A series of twenty-five large astronomical drawings, intended for the use of schools and colleges, is now in process of preparation, and will soon be issued by Messrs. J. H. Bufford's Sons, of Boston, who have reproduced in chromo the best of the drawings exhibited at Philadelphia
The numerous drawings of Mars obtained during the favorable opposition of the present year will enable me to perfect the map of Mars, or at least that of its southern hemisphere.
During the next year it is intended to continue observations on the physical appearance of the sun, etc. Mars will be followed as long as possible for the study of its climatology. Saturn will be closely watched for the phenomena exhibited at the disappearance of the ring. The study of Jupiter, commenced two years ago, will be continued. The study of the moon will also be continued, with a view to make the needed corrections to its existing maps, and with the intention to give at some future time a general view of our satellite as it appears at the most favorable moments. The study and delineation of the clusters and nebulæ will be continued, with the hope that, some day, means of publishing the results will be found.
Dearborn Observatory, Chicago, Ill.
Director. In reply to your circular requesting information in regard to the work, etc., of the Dearborn Observatory, I beg to say: Since July of the present year I have been using (unofficially) the 181-inch