44 



ASTRONOMICAL PHENOMENA AND PEOGEESS. 



miles, and its period thirty hours and fourteen 

 minutes. The inclination of their orbits to the 

 plane of the ecliptic is about twenty-five de- - 

 grees. 



Before the discovery of these satellites the 

 determination of the mass of Mars was a prob- 

 lem of much difficulty, the planet being so 

 small as to have little effect in disturbing the 

 motions of other bodies. Burckhardt's deter- 

 mination gave the ratio of its mass to that of 

 the sun as 1 to 2,680,387. Leverrier, after im- 

 mense labor, found the ratio to be that of 1 

 to 3,000,000 a close approximation to New- 

 comb's value derived from observations of the 

 exterior satellite, viz., 869 ^ 0(><) , that of the 

 sun being unity. The density corresponding 

 to a diameter of 4,200 miles, this value of the 

 mass is 0.715. 



The Martial satellites are the smallest mem- 

 bers of the planetary system hitherto discov- 

 ered. Prof. Newcomb, on the assumption that 

 their surfaces have the same reflective power 

 as that of Mars, infers that their diameters 

 cannot much exceed ten miles. 



The most remarkable fact in regard to these 

 bodies is the extremely short period of the in- 

 ner satellite, which completes three revolutions 

 in less than a Martial day. It seems difficult 

 to reconcile this rapidity of motion with the 

 nebular hypothesis as proposed by Laplace. 



Within four months from the date of their 

 discovery these diminutive bodies were lost to 

 view by reason of the increasing distance of 

 Mars from the earth. Fortunately, however, 

 Prof. Hall had secured about fifty observations 

 of each, by the discussion of which he will be 

 enabled to determine the elements of their or- 

 bits with a good degree of accuracy. The sat- 

 ellites will not probably be again observed till 

 1879. 



New Minor Planets. Since the issue of our 

 last volume the following names have been 

 given to minor planets discovered before 1877: 

 No. 150, Nuwa; 161, Athor; 162, Laurentia; 

 163, Erigone ; 164, Eva ; 168, Sibylla ; and 169, 

 Zelia. Nine new members of the group were 

 discovered daring the year, bringing the num- 

 ber up to 178 : Myrrh a, No. 170, was first seen 

 by M. Perrotin, at Toulouse, on the 10th of 

 January; No. 171 by Borelly, at Marseilles, 

 January 13th; Nos. 172 and 173 by the same 

 astronomer, February 10th and August 2d; 

 No. 174 by Watson, at Ann Arbor, September 

 3d ; Idunna, No. 175, by Peters, at Clinton, Oc- 

 tober 13th ; No. 176 by Henry, at Paris, No- 

 vember 5th; No. 177 by Palisa, at Pola, No- 

 vember 6th ; and No. 178 by Watson, at Ann 

 Arbor, November 12th. Hind, of London, 

 Borelly, of Marseilles, and Palisa, of Pola, are 

 now each credited with ten asteroids ; Gold- 

 schmidt with fourteen, Luther with twenty, 

 Watson with twenty-one, and Peters with twen- 

 ty-^seven. The whole number is distributed 

 among thirty-two observers. The elements of 

 those recently discovered, so far as published 

 ap to November, 1877, are as follows: 



It will be noticed that the number of aster- 

 oids discovered per annum is now gradually 

 decreasing. Thus, the numbers in 1875, 1876, 

 and 1877, were 17, 12, and 9, respectively. 

 Those recently discovered are small, generally 

 of the twelfth or thirteenth magnitude. The 

 orbit of Eva, No. 164, is remarkable both for 

 its eccentricity and inclination. 



The Elements of Gerda,. In the Astrono- 

 mische Nachrichten for November 10, 1877, we 

 find an interesting discussion of the observa- 

 tions of Gerda, the 122d member of the group, 

 by John N. Stock well, Esq., of Cleveland, Ohio. 

 This planet was discovered by Dr. Peters, at 

 Hamilton College, New York, in 1872, and the 

 observations of that year extend from the 31st 

 of July to the latter part of September. Ob- 

 servations were also obtained in 1873, 1876, and 

 1877. Mr. Stockwell obtained elements which 

 almost perfectly represent the entire series of 

 observations excepting those of 1873. It was 

 impossible, however, to find an orbit which 

 would harmonize the observations of that year 

 with those of 1872, 1876, and 1877. The con- 

 clusion was accordingly reached that the planet 

 observed for Gerda in 1873, not far from its 

 computed place, was really a different body 

 never before observed. In order to test this 

 question, Mr. Stockwell computed elements 

 from the observations of 1873 alone. The ele- 

 ments of the two orbits are as follows : 



EPOCH, 1873, NOVEMBER, 7.0 M. T., WASHINGTON. 



Planet of 187S. 



Mr. Stockwell thus concludes his interesting 

 discussion : 



If we compare these elements, we shall at once per- 

 ceive that four elements of the two orbits are almost 

 identical, namely, tlie mean distance, the eccentrici- 

 ty, the inclination, and the longitude of the node ; 

 while the transverse axes form an angle of about five 

 degrees with each other, and the mean anomaly of 

 Gerda is greater than that of the other planet by 

 more than five and a half degrees, and its mean Ion- 



