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eses, the conclusion was that, to observe the planet in transit, astronomers must wait till 1881 or 1885, although there is a possibility of a transit in 1877. It has been suggested that the total solar eclipse of 1878 will be a favorable opportunity to search for it; and if an approximate position of it for that time is given, the planet must be sure of detection, if it really exist.
Lassell, of England, examined Venus on the 12th and 13th of July for the purpose of seeing the unilluminated portion of the disk, but he was not successful.
Ertborn, of Antwerp, publishes in the Bulletin of the Belgian Academy a series of observations on spots on Venus.
Trouvelot, of Cambridge, is still pursuing his observations of the planets. During the present year he has made 112 sketches of Jupiter, 80 sketches of Mars, and several of Saturn. The weather has been unfavorable for Mars, and a quiet atmosphere has not yet been obtained. A spot which appeared on Jupiter April 15 is still visible, and has been observed by Trouvelot twenty times. The adopted period of rotation does not agree with that indicated by the spot. If the adopted period be correct, the spot has a retrograde proper motion of great regularity, “almost too regular,” as M. Trouvelot remarks.
Mr. Brett has published speculations on the "specular reflection” of Venus, the main idea of which is that Venus reflects the sunlight from a vitreous envelope, much as a thermometer-bulb would do. Mr. Brett suggests to observers of the next transit of Venus the propriety of looking in the globe of Venus for a reflected image of the earth, which will appear as a “minute nebulous speck of light.” This “nebulous speck” would be less than one fiftieth of a second of arc in diameter. Considering the difficulty of seeing Venus herself when very close to the sun, the hope of carrying out the provisions of this plan is rather a forlorn one, particularly as the light of this “speck” is diminished by reflection, and is to be seen close to a bright background.
On December 7,1876, Professor Hall, of the Naval Observatory at Washington, discovered on the disk of Saturn a brilliant oval white spot, which was observed to move across the disk for about an hour. It was central at 6 h.18 m. Washington mean time. Information was sent to various observato
ries in the United States, and observations were received from Edgecomb at Hartford, Mitchell at Vassar College, Boss at Albany, and Clark at Cambridge. It was first seen by Monckhoven, of Gand, December 6, at 22 h. 15 m. sidereal time, and was then about central. It should be noted that the rotation time of Saturn's ball, as given in many modern books (10 h. 29 m.), belongs to the ring (Laplace, “Mécanique Céleste"), while the true rotation time is near that given by Sir William Herschel (10 b. 16 m. 0.44 s.). Observations of this bright spot on Saturn were obtained through sixty-one revolutions of Saturn's ball. The resulting rotation time is 10 h. 14 m. 23.8 s.+2.30 s., which differs from Sir William Herschel's determination (10 h. 16 m. 0.4 s.) by less than 2 m.
Marth, of London, continues the publication of an extended ephemeris of the satellites of Saturn. These objects are observed by Hall, of Washington, at Greenwich, by Pratt at Brighton, and by Pritchett, of Glasgow, Missouri.
Professor Hall has given in the Astronomische Nachrichten elements and an ephemeris of Hyperion, the faint satellite of Saturn, derived from his own observations. Although these elements are regarded only as provisional, the inclination in particular requiring further observations to determine it, they are very close approximations, as is shown by the accordance of the ephemeris with the Washington observations of 1877.
With regard to Hall's elements of Hyperion, Hind remarks that they lead to the following numbers, assuming the solar parallax as 8.86": mean distance, 914,000 miles; least distance, 800,000 miles; greatest distance, 1,028,000 miles.
In Comptes Rendus (March 26), Tisserand gives the results of his observations of the five interior satellites of Saturn. Mimas has been observed five times, Enceladus seven times, etc. Tisserand gives the apparent diameter of the ring, as deduced from observations of three of the satellites, as below: Tethys, 40.45"; Dione, 40.61"; Rhea, 40.47"; mean, 40.51" —which shows that the method of observation adopted (William Herschel's and Lassell's) is susceptible of great accuracy.
Professor Hall read to the Philosophical Society of Washington a paper on the shape of the shadow of the ball of Saturn on the ring, in which mention was made of the abnormal direction of the curvature of the bounding-line of the shadow, it being now convex towards the ball, instead of concave. The abnormal figure of this shadow has often been noticed, and is corroborated by many independent observers. In particular the drawing of the shadow by M. Trouvelot, October, 1874, is undoubtedly correct, as other drawings made at the same time by other observers give the same appearance.
Todd, of Washington, has prepared a continuation of Damoiseau's tables of the satellites of Jupiter, which extends to 1900. This has been printed by the American Ephemeris in a quarto of forty pages, and will be sent to any astronomer having a copy of Damoiseau. The errata in Damoiseau's tables found by Hind, Kendall, and Todd, respectively occupy nearly three quarto pages. The British Nautical Almanac for 1881 contains tables with a similar object by Professor J. C. Adams.
An outer satellite of Mars was observed by Professor Asaph Hall, U.S.N., at the United States Naval Observatory, on the night of the 11th of August, 1877. Cloudy weather prevented the certain recognition of its true character at that time. On August 16 it was again observed, and its motion was established by observation extending through an interval of two hours, during which the planet moved over thirty seconds of arc.
An inner satellite was first observed on the night of August 17, also by Professor Hall. Both were discovered with the 26-inch telescope made by Alvan Clark and Sons.
On Saturday, August 19, the discoveries were telegraphed to Alvan Clark and Sons, Cambridgeport, Massachusetts, in order that, if the weather should be cloudy at Washington, they might confirm the existence of the satellites with the 26-inch telescope of Mr. M'Cormick, which is in their hands.
These discoveries were confirmed by Professor Pickering and his assistants, at Cambridge, Massachusetts, with the 15-inch telescope, and by the Messrs. Clark, at Cambridgeport, with a 12-inch glass.
On August 19 the discoveries were communicated to the Smithsonian Institution, by which they were announced to the American and European observatories. The period of the outer satellite is about 30 h. 18 m.; of the inner, 7 h. 35 m. The inner satellite is intrinsically the brighter, and the outer one has been seen with the 9.6-inch Munich equatorial at Washington. The most remarkable point of this important discovery is the short period of the inner satellite, which is only one third as long as that of Mimas, the innermost satellite of Saturn, hitherto the object having the shortest period in the solar system.
Apart from the physical interest of these brilliant discoveries, these satellites will furnish an accurate determination of the mass of Mars. From the observations of the first nine days this mass appears to be yoy000. The discussion of all the observations will change this somewhat.
A curious fact about the relative visibility of these satellites in various European telescopes is noticed elsewhere. Photometric measures of the satellites of Mars have been made by Professor Pickering and Mr. S. C. Chandler.
The series of observations made by Professor Hall on the moons of Mars ended October 31, the planet having receded to a distance at which they become invisible, even with the 26-inch refractor. Not until 1879 will there be any opportunity to see them again, and that will not give nearly so good a view as the past season. Professor Hall has secured fifty-one observations of the outer (Deimus) and forty-six of the inner satellite (Phobus).
A passage in the 15th book of the “Iliad," where Ares is preparing to descend to the earth, has suggested these names for the two satellites of Mars, which names, it is understood, Professor Hall has approved :
«« "Ως φάτο και ρ' ίππους κέλετο Δεϊμόν τε Φόβον τε
Ζευγνύμεν” which Pope renders
“With that he gives command to Fear and Flight
To join his rapid coursers for the fight.” Deimus and Phobus are the names adopted.
Todd, of Adelaide, Australia, has made an important series of observations of the phenomena of Jupiter's satellites. Besides the record of the times of the phenomena, notes on the physical appearances of Jupiter and the satellites are given. “ On one or two occasions when a satellite has been on the point of occultation it has appeared as if seen through the edge of the planet, as if the
latter were surrounded by a transparent atmosphere laden with clouds."
Dr. Meyer, in the V. J. S. of the Philosophical Society of Zurich, has an interesting résumé of the history of the discovery of Neptune, which is one of the best of the shorter accounts of this discovery; and in No. 37 of the Astronomische Mittheilungen he gives a brief but excellent sketch of the history of double stars, together with a series of measures and an investigation of the orbit of 2 634.
The Astronomische Nachrichten also contains an account by Galle of the discovery of Neptune.
Peters, of Clinton, notes a striking similarity between the orbits of Gerda (122) and Urda (167), their elements being alike except in one point. They move in one orbit about the sun, in the same periodic time, but are about 180° apart.
In the Smithsonian Report for 1876 Kirkwood has a statistical paper on the asteroids, in which the distribution of their perihelia, etc., is considered, and the analogies of the elements of their orbits are noted, and the same subject has been considered by Luther.
In a note by the veteran observer of asteroids, Luther, it appears that in the last twenty-nine years he has made no less than 819 observations of 98 asteroids !
Mr. Stockwell, of Cleveland, in studying the orbit of the asteroid Gerda, which has been observed in 1872, 1873, 1874, 1876, and 1877, finds that the ensemble of the observations leads to corrections to the elements which are quite inadmissible. The omission of the observations of 1873 leads to elements which almost perfectly represent the observations of 1872, 1876, 1877, but leave residuals of 27' (a) and 9' (8) for 1873. Using the 1873 observations alone, elements are obtained which satisfy them within less than 1" in both coordinates. The two sets of elements are closely alike in four elements, but the major axes make an angle of 5° or more. It is probable, according to Mr. Stockwell, that the planet of 1873 was not Gerda.
We have had to record the rediscovery of Maia (66), and by a similar process Camilla (107) has also been found. Schulhof prepared an ephemeris from January 8 to February 25 from the various systems of elements heretofore determined. That the uncertainty of this was enormous may