310 SCIENTIFIC RECORD FOR 1882. 



The disk of Jupiter. — Prof. G. W. Hough's annual report as director of 

 tlie Dearborn Observatory at Chicago, for the year 1882, is mainly de- 

 voted to the reduction and discussion of the numerous series of observa- 

 tions on the spots upon the disk of the i)lanet Jupiter, made with the 

 18i inch refractor, including measures for position of the great red spot, 

 of equatorial white spots and other markings, and angles of position of 

 the equatorial belt. The observations extend over the period from 

 September, 1879, to March, 1882. Those made in 1879 and 1880 showed 

 that the red spot was retrograding with accelerated velocity, and this 

 drifting has continued with such uniformity that Professor Hough con- 

 eiders "the iiosition of the spot at any future period can be very accu- 

 rately computed." It was found that all the observations could be fairly 

 represented by a period of rotation, varying directly with the time, 

 and the discussion leads to the following formula: (1879, September 

 25 + « X 0.00209s.,) which gives 9^ 55™ 35«.9 for the mean period between 

 September 25, 1879, and March 29, 1882, comprising 916 days, or 2,214 

 rotations of the planet. 



Hence, it is inferred that the apparent rotation -period has increased 

 about four seconds since the opposition of 1879, showing a total drift 

 of the red spot in longitude of 40,000 miles ; and Professor Hough 

 regards his observations as evidence that the great red spot is not the 

 solid portion of the planet. "An immense floating island," nearly 30,000 

 miles in length, and more than 8,000 in breadth, has "maintained its 

 shape and size, without material change, during more than three years." 

 He has failed to recognize any ftiding of the color of the spot, which, 

 on February 2 in the present year, he judged to be a light pink, as 

 formerly. Although the dimensions of the spot may not be said to 

 have materially changed, the micrometrical measures do indicate a 

 diminution in length to the extent of 0".95 between the oppositions of 

 1879 and 1881, at which latter epoch it was 11".30 (reduced to Jupiter's 

 mean distance). 



The direction of the south edge of the equatorial belt was nearly 

 parallel with the planet's equator, as given in Marth's ephemeris; the 

 north edge of this belt was found to be slightly concave. 



The elliptical wiiite spots Avere more numerous in 1882 than previ- 

 ously, but, with the exception of two situated south of the red spot, they 

 were seen with difficulty, and were onlj' measurable under the best 

 vision. The two spots named were observed systematically during the 

 three months from November 21, 1881, to February 23, 1882. The fol- 

 lowing of the two appeared to be at rest relatively to the red spot from 

 I^Tovember 22 to December 6, and subsequently to di-ift in the direction 

 of rotation to the extent of about 41° j the average drift during the 

 last two months was at the rate of fifteen miles per hour. The preced- 

 ing spot also did not retain the same relative position in longitude with 

 respect to the great red spot. Professor Hough adds: "The observa- 

 tions of the small white spots during 1880 and 1881 prove that the 



