92 



SCIENCE. 



[N. S. Vol. XVII. No. 420. 



lite over the red spot. The satellite, which 

 was invisible during transit, when projected 

 on the spot appeared as bright as when off 

 the disk. On the contrary, when satellites 

 transit the belt they are invisible. (2) 

 Egg-shaped white spots from 2,000 to 5,000 

 miles in diameter. These spots I have 

 found in north latitude 13 to 37 degrees 

 and in south latitude from 18 to 27 

 degrees. These objects do not look like 

 clouds, and so far as we know they do not 

 change their shape during the six months 

 while under observation. They are also 

 very stable in latitude and give a rotation 

 period of 9"^ 55™ +. (3) Small black spots 

 seen on the belts or entirely separate. These 

 objects give a rotation period of 9^ 55"" -j-, 

 but on one occasion in latitude 20 degrees 

 north I found a short period. (4) The 

 dark matter forming the system of belts 

 including the equatorial belt and the so- 

 called polar belts, which also give a rota- 

 tion period of 9^ 55™. (5) The white spots 

 which give a rotation period of 9^* 50™. 



It seems to be the opinion of most writers 

 on Jovian phenomena that the planet is yet 

 at a high temperature, but not self-lumin- 

 ous. The high temperature is favorable 

 for the explanation of some of the phe- 

 nomena observed. I have long held the 

 opinion that a simple atmospheric theory 

 was not sufficient. The greater luminosity 

 of the center of the disk indicates absorp- 

 tion of light, probably due to an extensive 

 atmosphere. The white spots Avhich give 

 a rotation period of 9'' 50™ are of different 

 form and size from the egg-shaped spots 

 which give the period of 9"^ 55™ -{-. The 

 short period spots are greater in size and 

 irregular in shape, sometimes appearing 

 simply as a rift in the equatorial belt. 

 Having these facts before us, we can 

 formulate a theory which will fairly well 

 satisfy all classes of phenomena. 



I assume that the visible boundary of 



Jupiter has a density of about one half 

 that of water. This medium is in the 

 nature of a liquid; in it are located the 

 great red spot and the egg-shaped white 

 spots. In such a medium all motions in 

 longitude and latitude would be slow and 

 gradual, and the shape and size of the 

 object would have great permanency. 

 The equatorial belt and the so-called polar 

 belts may be located on the surface or at 

 a higher level than the red spot. In the 

 middle latitude within twenty degrees of 

 the equator the higher atmosphere carries 

 a layer of dark matter in the direction of 

 the rotation of the planet at a velocity of 

 about 250 miles per hour, making a com- 

 plete circuit around the planet in 44 days. 

 In this envelope are formed the openings 

 which we call white spots and, by unequal 

 distribution, black spots. The great bay 

 in the south edge of the equatorial belt may 

 be accounted for by assuming that the 

 great red spot is at a lower temperature 

 than the medium in which it floats, and by 

 its lower temperature condensing a portion 

 of the vapor composing the belt. In 1882, 

 when the edge of the belt drifted south, it 

 did not come in contact with the spot at any 

 point, although it advanced at times be- 

 yond the center. In 1883 I stated that the 

 spot seemed to have a repelling influence on 

 the belt. During the past twenty years, 

 when the belt and the spot were in prox- 

 imity a depression was formed in the belt 

 directly opposite, which was of the same 

 form as the contour of the spot. The belts 

 may be assumed to be some sort of vapor of 

 considerable density. The cloudlike mat- 

 ter, which in the eqiiatorial regions is mov- 

 ing over the surface at the rate of 250 miles 

 per hour would account for the minor 

 changes on the surface of the equatorial 

 belt. I think the theory I have given 

 offers a more plausible explanation of the 

 various phenomena observed than the off- 



