SOME PHYSICAL CHANGES ON THE SURFACE OF JUPITER. 681 



the aubject, and prints for the first time in one collection all the known official 

 documents, notices in accounts, passages in contemporary chronicles, or corre- 

 spondence in any way bearing upon John Cabot and his discoveries. Some of 

 these, drawn from Spanish and English sources, are new. The author adduces 

 the conclusions of Mr. Henry Harris, an American in Paris, who is at work upon 

 a new publication on Columbus, to support his own that the Continent of America 

 was discovered by Cabot in 1497, at least a year before Columbus found terra 

 fir ma. 



ASTRONOMY. 



SOME PHYSICAL CHANGES ON THE SURFACE OF JUPITER. 



BY PROF. C. W. PRITCHETT, MORRISON OBSERVATORY. 



The changes which have taken place, within the last three years, on the ap- 

 parent surface of the planet Jupiter, are really wonderful. To one who has seen 

 the giant planet but a few times in his life, and even to an^astronomer, who has 

 not noted from week to week the markings on his surface, a detailed account of 

 their changes would be almost incredible. Perhaps the phenomenon of the great 

 red spot, which became so conspicuous in July, 1878, and which still persistently 

 holds its place, has awakened an unusual interest in the study of his surface, but 

 certain it is, that never before, has his disc been so closely watched, and never 

 have so many phenomena been noted, in so short a time, as within the last three 

 and a half years. 



In this note my object is not to describe these changes, but specially to men- 

 tion an instance observed here on the night of December 23rd. It chanced to 

 be one of the finest nights of the whole year. The surface of the great planet 

 was rarely ever seen under better conditions of altitude and atmosphere. Every 

 line and marking came out with a distinctness which was a wonder even to an 

 experienced observer. The great red sjJot, by the Jovian rotation, was approach- 

 ing the central meridian of the disc ; and I had begun my usual observation of 

 the transit of the preceding end, when my attention was called to a condensed 

 white nucleus situated in the north margin of the most southern of the equatorial 

 belts. The threads of the Filar Micrometer, had been adjusted to the rotation 

 axis of the planet, by the ephemeris of Mr. A. Marth. (Month. Not. R. A. S ^ 

 Vol. 41, No. 7). One fixed thread was placed on one extremity of major axis of 

 spot, and the movable thread was placed on the other extremity of that axis, and 

 these threads were kept to this position by the driving clock, and an adjusting 

 screw. At 7h. 7m. of local mean time the following end of red spot and the 

 bright nucleus were on the same thread, or the bright spot was on the same 



