ASTRONOMICAL PHENOMENA AND PROGRESS. 



gitude is greater by about seven-tenths of a degree. 

 Although the two bodies are apparently so close to- 

 gether, we must remember that an arc of their orbits 

 amounting to seven-tenths of a degree implies a dis- 

 tance of al)out 3,600,000 miles. It is perhaps impos- 

 sible to decide with certainty in regard to the iden- 

 tity of the planet observed in 1873 with that of Gerda : 

 the close similarity of most of the elements would 

 seem to indicate an identity, while the dissimilarity 

 of the other elements and the impossibility of rep- 

 resenting the observations indicate, perhaps with 

 equal force, a dissimilarity. If there are really two 

 planets moving in orbits so extremely near together, 

 it must happen in the course of time, unless their 

 mean distances are exactly the same, that they will 

 approach each other so closely that their mutual per- 

 turbations will cause them to unite and form a single 

 planet. 



Phenomena of Jupiter's Satellites. The 

 Monthly Notices of the Royal Astronomical 

 Society for April, 1877, contains an interesting 

 communication from Charles Todd, Esq., of the 

 Adelaide Observatory, South Australia, on the 

 phenomena of Jupiter's satellites, with notes on 

 the physical appearance of the planet. " On 

 one or two occasions," this astronomer re- 

 marks, " when a satellite has been on the point 

 of occultation, it has appeared to be projected 

 on the disk of the planet ; or rather, as it ap- 

 peared independently to my assistant (Mr. Ring- 

 wood) and myself, as if seen through the edge 

 of the planet, as if the latter were surrounded 

 by a transparent atmosphere laden with clouds. 

 I noticed this on two occasions, viz., on August 

 21st, at the disappearance of the first satellite, 

 when the satellite was distinctly seen on or 

 through the edge of the disk for about two 

 minutes before disappearance I say through 

 the edge of the disk, because the satellite was 

 less bright than in a similar position at a tran- 

 sit ; and again at the disappearance of the sec- 

 ond satellite on August 28th. Mr. Ringwood 

 also noticed it on August 12th and 19th, at 

 occultation of first and third satellites. In 

 each instance the planet was splendidly de- 

 fined better than I ever remember to have 

 seen it in England." 



In regard to changes observed in the appear- 

 ance of Jupiter Mr. Todd continues : " I was 

 much impressed on some nights with the sud- 

 den and extensive changes in the cloud-belts, 

 as though some tremendous storm was in prog- 

 ress on the planet's surface, changing the form 

 and dimensions of the cloud-belts in an hour 

 or two, or even less." 



The Physical Condition of Jupiter. The ob- 

 servations of Mr. Todd, especially those of Au- 

 gust 21st and 28th, 1876, appear to strengthen 

 the views advanced by Mr. Proctor in respect 

 to Jupiter's present condition. These views 

 are presented at some length in THB POPU- 

 LAR SCIENCE MONTHLY for May, 1877. The 

 appearance of Jupiter's surface, the motion 

 of its cloud-masses, etc., indicate, according to 

 Mr. Proctor, that the planet is much less ad- 

 vanced in its physical history than Mars and 

 the earth ; that it has a very extensive atmos- 

 phere, probably from 6,000 to 11,000 miles in 



depth; that the spots have proper motions 

 with respect to the surface, and do not indi- 

 cate the true rotation-period of the solid or 

 liquid planet ; that the nucleus is intensely hot ; 

 and, finally, that this giant member of our sys- 

 tem "may justly be described as a miniature 

 sun, vastly inferior in bulk to our own sun, 

 inferior to a greater degree in heat, and in a 

 greater degree yet in lustre, but to be com- 

 pared with the sun not with the earth in 

 size, in heat, and in lustre, and, lastly, in the tre- 

 mendous energy of the processes which are at 

 work throughout his cloud-laden atmospheric 

 envelope." 



The Rotation of Saturn. In the Astrono- 

 mische Nachrichten for August 16, 1877, Prof. 

 Asaph Hall gives a new determination of the 

 length of the Saturnian day. The value hith- 

 erto accepted, and said erroneously to be Sir 

 William Herschel's final determination, was 

 10 h - 29 m ' 16'-. 8 nearly fifteen minutes great- 

 er than the period found by Prof. Hall. On 

 the night of December 7, 1876, a bright spot 

 was noticed on the ball of Saturn. It was two 

 or three seconds in diameter, round and well 

 defined, and of a brilliant white color. From 

 December 7, 1876, to January 2, 1877, nineteen 

 observations were secured : twelve at Washing- 

 ton, by Profs. Hall, Eastman, and Newcomb ; 

 four at Cambridgeport, Mass., by Mr. A. G. 

 Clark ; one at Poughkeepsie, N. Y., by Miss 

 Mitchell ; one at Albany, N. Y., by Mr. Boss ; 

 and one at Hartford, Conn., by Mr. Edgecomb. 

 A discussion of these observations gives 10 h - 

 14 m> 23'-. 8 as the period of rotation, with a 

 probable error of 2"-. 3. Prof. Hall remarks, 

 however, that " this value has been found by 

 assuming that the spot had no proper motion 

 on the surface of the planet. Whether this 

 was really the case or not we cannot determine 

 from the observations." 



Appearance of Saturn's Rings. Prof. Hall, 

 of Washington, commenced a series of obser- 

 vations of Saturn's satellites in 1875, which he 

 continued till January, 1877. During this time 

 occasional attention was given to the system 

 of rings, especially after the publication of Mr. 

 Trouvelot's description of their phenomena as 

 observed by himself. Strangely enough, how- 

 ever. Prof. Hall has not been able to see the 

 slightest trace of certain peculiarities noticed 

 by Mr. Trouvelot. The former remarks that 

 during a summer in Washington there are not 

 more than six or eight nights in which the 

 26-inch refractor gives excellent images of Sat- 

 urn. " On these nights," he says, " the appear- 

 ance of the planet is very beautiful ; but my 

 experience is that on these rare nights one will 

 see fewer strange phenomena about the ring 

 and the shadows than when the images are 

 blurred and indistinct. Still I do not wish to 

 be understood as denying the reality of what 

 others have seen and described. I can only 

 say that during the past two years I have not 

 been able to see some of these things." Prof. 

 Hall adds: 



