312 PROCEEDINGS OF THE AMERICAN ACADEMY 



red spots, one larger tlian the other, each surrounded by a brilliant 

 and narrow white ring. I called the attention of the MM. Henri 

 to this fact, which both easily verified. The color of these two small 

 spots was not that of the equatorial belt, which is of a different shade 

 and much less intense, but precisely the same as that of the great red 

 spot, which they, with their bright ring, resembled in miniature. It 

 will be seen below that the pink color sometimes appears instantly in 

 different parts of the disk, and this even in high latitudes. 



Allowing for errors of observation, and taking them into account, 

 it is found that the period of rotation of the red spot is irregular, and 

 varies somewhat on certain days, while on others no variation is per- 

 ceptible. This shows that the red spot, like all other spots described 

 in this paper, is not fixed on the j^lauet, and changes place under the 

 action of internal or external forces. 



The mean period of rotation of this spot seems to have slowly 

 decreased for some time. From the end of September to the end of 

 December, 1878, the mean period of rotation is found to be 9^ So™ 

 43. 6P; from the end of December, 1878, to the beginning of January, 

 1880, the mean period was 9^ 55"" 36.85'. But from January, 1880, 

 to February, 1881, it is found to be Q^ 55" 38.96'. The mean period 

 of rotation from the whole being approximately 9*^ 55"^ 38.57'. 



Mark F. 



Besides the great red spot E, and the markings C and D, which were 

 conspicuous and permanent objects, other spots of shorter duration 

 have also been observed, and their proper motion carefully watched. 



One of the most characteristic among them appeared inside the 

 equatorial belt, close to its southern border. It consisted of a very 

 bright, round spot, forming the preceding extremity of one of the white, 

 cloud-like spots which constitute the middle zone of the equatorial 

 belt. This bright object protruded considerably southwards on the 

 rosy background of the equatorial belt, and as far as its southern 

 border, which it seemed sometimes to push out and swell at that 

 point. 



This spot, although it very likely existed before, was particularly 

 noted on Nov. 16, 1880, and was watched until it disappeared. 

 By going backward and examining the drawings anterior to that 

 date, it was found that one of the markings, much resembling the 

 mark F, was observed as far back as Aug. 8 of the same year, 

 although it was not so brilliant at that time as it has been since, if it 

 is the same spot. As it is thought to be the same object, I will give 



