Dec. 13, 1877] 



NATURE 



129 



OUR ASTRONOMICAL COLUMN 



The Satellites.— The following table presents at 

 one view the mean distances of the satellites from their 

 primaries, expressed in equatorial semi-diameters of the 

 latter, and founded upon the most reliable data hitherto 

 available : — 



The Earth. Mars. Jupiter. Saturn. Uranus. Neptune. 



T. 



ir. 



TIL ... — 



IV. ... — 



V. ... — 



VI. ... — 



VII. ... — 



VIII. ... — 



6027 ... 272 

 6 8i 



570 ... 2-98 ... 771 ... 14-55 



9'o7 •••■ 3"83 ••• 1075 ••• — 



14-46 ... 475 ••• 1763 ... — 



2544 ... 608 ... 23 57 ... — 



— ... 8-47 ... - ... - 



— ... 1967 ... — ... — 



— ... 24-80 ... — ... — 



— ...5728 ... - ... - 



It will be seen that the outer satellite of Saturn, 

 lapetus, is the only one revolving round its primary at a 

 distance similar to that of our moon, with respect to the 

 semi-diameter of the central body. The exterior satel- 

 lites of Jupiter and Uranus are similarly placed in this 

 respect, and as regards the former planet the reader will 

 remember a suggestion of Sir John Herschel's, that a 

 distant satellite, by which was intended one situate more 

 nearly, as our moon or the Saturnian satellite lapetus, 

 might be " worth a search." At the end of the last 

 century it was thought that if satellites of Mars existed 

 they might be " distant many degrees from the principal 

 planet," upon which idea the late Prof. D'Arrest argued 

 that a search after a satellite situate many degrees from 

 Mars would be an almost endless task ; and further, that 

 a satellite at a maximum digression of seventy minutes of 

 arc would have a sidereal period greater than the synodi- 

 cal revolution of the primary. The same astronomer 

 endeavoured to ascertam, at the opposition of 1864, to 

 what magnitude stars were visible in the vicinity of Mars 

 with the Copenhagen refractor, which has an aperture of 

 about eleven English inches. He considered that a satel- 

 lite as bright as the twelfth magnitude could hardly have 

 escaped him, and that objects of a fainter class were 

 only visible in such an instrument at distances of eight or 

 ten minutes, and in the case of Mars opportunities of 

 viewing a satellite in such position would occur compara- 

 tively seldom. Perhaps the more prevalent idea respecting 

 possible satellites of Mars, prior to their actual discovery, 

 was that they would be " very small and close to the 

 planet." (Hind, in " Solar System," p. 78.) 



Tycho Brake's Star of 1572. — It is to be hoped 

 that the vicinity of the famous star in Cassiopeia, with 

 which we are accustomed to associate Tycho Brahe's 

 name, may continue to receive frequent attention, and in 

 particular that the small star, which at present is so near 

 to the most accurate position we are able to obtain of the 

 star of 1572, may be assiduously watched and its bright- 

 ness determined from time to time by comparison with 

 its neighbours, and not merely by estimation of magni- 

 tude. It was Bessel who, as he states in a letter to 

 Olbers, in 1824, first engaged Argelander to work up the 

 position of the Nova Cassiopeiae, with all possible pre- 

 cision. Forty years later Argelander revised his calcula- 

 tions with improved positions for trie reference-stars, and 

 obtained a result differing in no material degree from the 

 earlier one. The small star alluded to is so near to 

 Argelander's last position |(differing only fifty seconds of 

 arc), as to be within its possible limits of error ; it is No. 129 

 of the catalogue of stars in the vicinity which was pre- 

 sented to the Copenhagen Academy in January, 1864, 

 and an eleventh magnitude on Bessel's scale. It will be 

 most readily identified by means of the star of the ninth 

 magnitude. No. 300 of Oeltzen's Catalogue from Argelan- 

 der's northern zones, the position of which for 1878-0 is 

 in R,A. oh. 17m. 32s., N.P.D. 26° 22'-6 ; the suspicious 

 object follows Argelander's star 29-65., and is south of 



it 10' 4". The place of Nova for 1878-0 is in R.A. 

 oh. i8m. 2-is., N.P.D. 26° 31' 43". 



The Austrian Comet-medal.— We have received 

 from the Imperial Academy of Sciences at Vienna, the 

 conditions upon which that body has resolved to renew, 

 until further notice, the prizes for the discovery of tele- 

 scopic comets, and which appear to be similar to those 

 originally issued in June, 1872. The awarding of a 

 prize, which will consist, according to the wish of the 

 receiver, in a gold medal or its money value of twenty 

 Austrian ducats, is connected with the following condi- 

 tions : (i) Prizes will be awarded only for the first eif^ht 

 successful discoveries in each calendar-year, for comets 

 that at the time of their discovery were telescopic, ie. 

 invisible to the naked eye, that had not been previously 

 seen by any other observer, and which could not have 

 been predicted, and it is important to observe that in the 

 case of independent discoveries priority is to be decided 

 by^the epoch of the first position. (2) The discovery must 

 be communicated to the Academy of Sciences imme- 

 diately, by telegraph, where practicable, otherwise by the 

 earliest mail, the Academy undertaking to make it known 

 without delay to several observatories. (3) This first 

 notice must necessarily contain the position and motion 

 of the comet as accurately as they are known, with the 

 place and time of discovery, and is to be supplemented at 

 the next opportunity by later observations. (4) If the 

 discovery should not have been verified by other ob- 

 servers, the prize will only be adjudged 'Svhen the 

 observations of the discoverer are sufficient for deter- 

 mining the orbit." (5) The prizes will be awarded in the 

 general sitting of the Academy held at the end of May in 

 each year, and in cases where the first intimation of the 

 discovery arrives between March i and May 31, the 

 award will be decided in the general May session in the 

 following year. (6) Application must be made for the 

 prize to the Imperial Academy within three months after 

 the first notice of discovery shall have reached it, later 

 applications being rejected. Finally, the astronomers of 

 the observatory of the University of Vienna are appointed 

 judges, whether the conditions in (i), (3), and (4) have 

 been fulfilled. 



GEOLOGICAL WORK OF THE U.S. SURVEY 

 UNDER PROF. HAYDEN DURING THE 

 SUMMER OF 1877 



'X*HE necessity of a careful examination of the various 

 -^ geological formations in the field, and a review by a 

 practical palaeontologist of the various districts that have 

 from year to year been surveyed by the different geologists 

 of this and other surveys, has been long felt. Such a 

 work, indeed, was imperatively necessary, before a con- 

 sistent and comprehensive classification of the formations 

 could be estabhshed. This duty was assigned to Dr. C. 

 A. White, the palseontologist of this survey, and he took 

 the field at the beginning of the past season and con- 

 tinued his labours until its close. The special duty with 

 which he was charged was to pursue such lines of travel 

 as would enable him to make critical examination of the 

 geological formations in succession as they are exposed 

 to view on both sides of the Rocky Mountain chain, and 

 also on both sides of the Uinta chain ; to collect and 

 study the fossils of these formations in such detail as to 

 settle, as far as possible, the questions of the natural and 

 proper vertical limits of the formations, their geographical 

 range, their correlation with each other, and to define 

 the palEeontological characteristics of each. 



He has pursued his researches with such success during 

 the past season as to demonstrate the necessity of con- 

 tinuing this class of investigations by various lines of 

 travel across what is generally known as the great Rocky 

 Mountain region, especially those portions of it that have 



