50 



ASTRONOMY, PROGRESS OF, IN 1894. 



condition of the planet, and, being caused by 

 snow, corroborate the theory of an atmosphere, 

 without which snow could not be produced. 

 Early in the season, when not so well situated for 

 observation as now, the snow cap at his south pole 

 was a conspicuous object, but as that has melted 

 under the summer sun, only the dark, somber 

 planet may now be seen. When his winter is 

 prolonged one will appear at the north pole. 



Jupiter. Dr. Edward E. Barnard, of Lick 

 Observatory, has devoted much time to the de- 

 termination of the equatorial and polar diame- 

 ters of Jupiter, as observed with the 36-inch 

 refractor, using uniformly a magnifying power 

 of 520. The mean results of all his measures 

 are as follow : Equatorial diameter, 38'532" 

 0-024 = 90,190 miles; polar diameter, 36-112" 

 0-032 = 84,570 miles. This, which he thinks is 

 very near their true value, differs from other ob- 

 servations by an entire second, or over 2,000 

 miles, and leads him to the conclusion that the 

 determination of the true size of Jupiter is not 

 an easy problem. 



In relation to the spots that often suddenly 

 appear on Jupiter's disk, Prof. Gr. W. Hough, of 

 the Evanston (111.) Observatory, says: "They 

 appear in a medium, having a depth of some 

 thousands of miles, and also have a freedom of 

 motion in this medium. This points to the 

 conclusion that the planet is gaseous, which is 

 borne out by the gradual fading of the light of 

 the satellites when projected on the disk of the 

 planet." 



Jupiter's Fifth Satellite. Dr. Barnard, 

 the discoverer, by a prolonged series of observa- 

 tions, determined the values of its eastern elonga- 

 tions during 1893-'94, and finds the mean value 

 to be 47'785"0'044", corresponding to a distance 

 from Jupiter of 111,910 miles, or about 67,000 

 miles from the surface. He finds, however, the 

 elongation a varying quantity. No observations 

 could be obtained of its western elongations. 

 The sidereal period of revolution, from a mean 

 of all the observations, he deduces as ll h 57 m 

 22-618 8 0-013, in an eccentric orbit. M. Tisse- 

 rand finds that the major axis of the orbit must 

 make a complete revolution in the astonishingly 

 short period of five mont-o. The motion of this 

 satellite about its primary is 16'4 miles a second, 

 making it the most rapidly revolving satellite 

 known even twelve times swifter than the rate 

 of Phobos, the inner satellite of Mars. Prom 

 several considerations he has been led to believe 

 that it can not exceed one hundred miles in di- 

 ameter, and may be less. If it were greatly over 

 one hundred miles, its shadow on the planet 

 could be seen with the 36-inch telescope. 



Diameter of Saturn. The exact determina- 

 tion of a planet's diameter, owing to obstacles 

 of an optical diameter, is a difficult problem. 

 " The secondary spectrum of the refractor," says 

 Prof. Wmimnn Struve. "causes want of defini- 

 tion of the boundaries of the planet's disk ; this 

 effect is increased by diffraction and by unsteadi- 

 ness of the air. In addition to these* and other 

 difficulties, the micrometer employed seems to 

 influence the result." A series of results from 

 1826 to 1887 shows in the case of Saturn an 

 uncertainty of at least a half second, the best 

 heliometric observations giving its equatorial 

 diameter as 17-1", and the axis of the ring as 



39-5", while best filar micrometer measures give, 

 respectively, 17'7" and 40-3". A series of 93 

 measurements made with the 30-inch Pulkowa 

 refractor, from 1889 to 1892 inclusive, for the 

 determination of the orbits of Rhea and Titan, 

 gives 17-471" for the equatorial diameter of Sat- 

 urn, and 39-2" for .its ring. Similar uncertain- 

 ties obtain with the other planets. 



Variables. The director of Harvard College 

 Observatory, Prof. E. C. Pickering, in his annual 

 report, says that in a photograph of the cluster 

 Omega Centauri, Prof. Bailey counted on a 

 region the size of the sun 7,000 stars, two of 

 which have been found to be variables. In " As- 

 tronomische Nachrichten," Prof. Pickering an- 

 nounces that Mrs. Fleming has discovered four 

 new variables, one, a star in Sculptor, right as- 

 cension O h 10-4 m ; declination 32 36', varying 

 from 6-5 to 10th magnitude in 366 days. Another 

 is in Scorpio, right ascension 16 h 50'3 m ; declina- 

 tion south, 30 26', varying from 7'3 to 11-6 in 

 278 days. The third is in Ophiuchus, right as- 

 cension 17 h 14'5 m ; declination north 1 37', vary- 

 ing in 348'4 days from 8-5 to 12'5 in magnitude, 

 and the fourth was found in Aquilla, right as- 

 cension 19 h 46'5 m ; declination north 4 13', vary- 

 ing from 9'5 to 12th magnitude in about a year. 



Dr. S. C. Chandler discovered on Aug. 5 a re- 

 markable variable star of short period, which has 

 received the name Z. Herculis. The following 

 synopsis will show the rapidity of its fluctua- 

 tions, as observed in Leyden : On Sept. 18, 1894 

 at 7 h 45 m , magnitude 4'87 ; at 8 h 7 m , magnitude 

 3-91 ; at 8 h 45 m , magnitude 3-58 ; at 9 h 41 m , mag- 

 nitude 5-25; at 10 h 12 m , magnitude 6'38; at ll h 

 5 m , magnitude 7'92. On Sept. 20 at 7 h 54 m , 

 magnitude 8*09 ; at 9 h 34 m , magnitude, 8'26. On 

 Sept, 22 at 7 h 17 m , magnitude, 6; at 8 h 44 m , 

 magnitude 3-25; at 10 h , magnitude 6'33. On 

 Sept. 24 at 7 h 24 m , magnitude 8'09 ; at 8 h 30 m , 

 magnitude -59. This star, which is of the Al- 

 gol type, is Durchmusterung + 15 3311 ; right 

 ascension (1855) 17 h 51 m 34 s ; declination + 

 15 9-3'. 



Temporary Stars. The history of astronomy 

 includes about a dozen well-authenticated in- 

 stances of the appearance of new stars, and it is a 

 curious fact that the last two, the one in Auriga 

 and that in Norms, should have manifested 

 themselves within two years of each other, and 

 that the earliest record of their existence should 

 in both cases have been made by photography. 

 These stars, like all of this character, appeared 

 suddenly. Stars of this kind were formerly sup- 

 posed to be very rarely seen, but this number 

 shows them to be not so unfamiliar. Examina- 

 tion of their spectra showed that each prominent 

 bright line in the Nova Auriga had a corre- 

 sponding bright line in Nova Normse, and that 

 every hydrogen bright line had a companion 

 dark line by its side in both spectra, the dark 

 line in every instance being toward the violet 

 end of the spectrum. The Nova Normae was 

 discovered on Oct. 26, 1893, by Mrs. Fleming, of 

 Harvard College Observatory, during the in- 

 spection of a photograph taken on July 10, 1893, 

 at the observatory founded by Harvard at Are- 

 quipa, Peru. The spectrum of this new star is 

 declared by Prof. Campbell to be unmistakably 

 nebulous. The behavior of Nova Auriga has 

 been unique, the cause of which is not apparent. 



