OF ARTS AND SCIENCES. 301 



parallelism with the equatorial belt, at 10^ 20"", the pink color 

 forraed a wide belt extending from 10° of north latitude to 45° of 

 south latitude, being therefore 55° in breadth. 



Not only that zone of Jupiter was in commotion, but the whole of 

 the southern hemisphere participated in it up to the pole, as proved 

 by the total change of the markings, and the swelling of all the bands 

 to higher southern latitudes on their following side. One of the 

 bands, which on the western limb was at 30° south, was swollen to 

 the south pole on its following extremity. It is to be noted that, iu 

 this great disturbance, the bands, although enormously swollen on the 

 following side, still maintained the same distance from each other ; 

 each one keeping pace with the other, and following it in all its sinu- 

 osities, the effect being apparently the same as if a wedge had been 

 driven from east to west between the upper border of the equatorial 

 belt and the oblique band described. On many occasions in 1876, this 

 continuous parallelism between the different bands in the midst of dis- 

 turbances was observed, as if the force causing the disturbance had 

 been moving from east to west, between the vapory envelope of 

 Jupiter, and pushing it aside in its passage, as a ship parts the waves 

 of the ocean. 



On the following day no traces of this great storm appeared ; 

 but everything seemed quiet, the equatorial belt having resumed 

 the same appearance it had on the 25th, before the commotion oc- 

 curred. 



If we determine the period of rotation of Jupiter from the observa- 

 tions of this angular marking, which will be called B, it is found to be 

 very nearly two hours, a period which is very far from agreeing with 

 that found by the observations on the mark A above described, and 

 the adopted period until lately, viz. 9'' 55" 4P. The last two periods 

 may be called the periods of calm, while the first may be called the 

 period of distui'bance. 



Mark C. 



In 1876 the observations on Jupiter were discontinued after Oct. 

 19, and resumed after conjunction, on April 11, 1877. On that day a 

 very characteristic mark, resembling a step seen in profile, was observed 

 on the southern border of the equatorial belt, which at one point was 

 deflected at a right angle, the western portion of the belt, or preceding 

 side, being narrower than the eastern or following side. 



This step-like marking, which will be called C, was a new fonn, 

 which had not once been seen in 1876, It remained visible through- 



