50 Kansas Academy of Science. 



THE ROTATION PERIOD. 



In measuring the rotation period both transits over the 

 central meridian and elongations of the marking were ob- 

 served. For the transit observations the double value of the 

 equatorial diameter v^as measured as usual, and the microme- 

 ter set to one-fourth this value minus one-half the wire correc- 

 tion. As the marking approached the central meridian it was 

 tested by setting first the right, then the left wire tangentially 

 till the eye was satisfied that the central meridian had been 

 reached and the time recorded to the nearest tenth of a minute. 

 The elongation measures were reduced to the time of central 

 transit. The reductions show that the elongations will give as 

 accurate values of the rotation period as the transits, if the 

 seeing is good enough to permit rapid measurement. 



From an elongation of the round spot, longitude 309.8°, lati- 

 tude 15.0° north, on September 21, and a transit of October 29, 

 the value T = 9'' 55™ 40.76^-, or an acceleration of 1.1^ per de- 

 gree of latitude in this region. 



THE POLAR COMPRESSION. 



Twenty-five observations were made for the polar compres- 

 sion, of which ten were rejected on plotting the risiduals. 

 From the fifteen remaining, the value 1 17.4 ± 1/270.3 was 

 obtained. This is a probable error of 8.4 percent. 



THE GREAT RED SPOT. 



The "great red spot" was quite distinct at times, showing a 

 dull brick-red color. Its measured position was longitude 

 131.7% latitude 23.0" south, length 29,275 miles. A peculiar 

 group of plumes follows it. The ends of the spot had quite 

 sharp points. 



THE SATELLITES. 



On two nights the images were quite free from flaring. The 

 means of the measures are : I = 2614 mi., II = 2233 mi., Ill 

 = 3908 mi., IV = 3422 mi. 



Markings were observed on III and IV. Attention was 

 especially attracted to III. On two occasions, October 21.419 

 and October 29.458 C. S. T., a marking was distinctly seen. 

 The angle the straight side of the marking makes with the 

 plane of the planet's equator being 70 \ It will be noticed that 

 the time between the observations is nearly equal to the rev- 

 olution period of the satellite, which seems to indicate that the 



