A Few Notes on Jupiter. 



By "W. Eenest Cooke, B.A., Assistant Astronomer. 



[Read February 2, 1886.] 



Plate I. 



The phenomena revealed in the Jovian system are as remark- 

 able as they are obscure, and evidently denote the existence of 

 forces in an intensity of manifestation utterly unknown in this 

 world at the present time. The condition of Jupiter's surface 

 is a subject for interesting speculation. "We cannot possibly 

 say with certainty what that condition may be, but have reasons 

 for believing that some of the whiter portions, at all events, 

 consist of a semi-transparent vaporous substance. Mr. Todd, 

 our Government Astronomer, was the first to point out this 

 peculiar semi-transparent property ; for on one occasion, when 

 watching an occultation disappearance, he distinctly saw the 

 satellite through the planet's limb, and could still see it when 

 its light must have pierced through more than a thousand miles 

 of the surface matter of the planet. This was confirmed 

 by subsequent observation and after the fact had been 

 pointed out several other astronomers, including Mr. Ellery, 

 of Melbourne, observed the same effect. I have witnessed 

 this phenomenon on several occasions during the past two or 

 three years, when the definition of the limb has been so re- 

 markably sharp as to utterly preclude any idea of optical illu- 

 sion. Ths whole of the planet's surface, however, is not wmite, 

 but there are well-marked dark belts, which seem to keep their 

 shape more or less the same for a number of years, and dark 

 and bright spots that disappear and reappear in a remarkable 

 manner, some apparently suddenly, but most, I think, gradu- 

 ally. The principal belts (all of which are almost parallel to 

 the equator) are two dark ones about five to ten degrees on either 

 side of the equator, and inclosing a broad equatorial light 

 band, with many interesting markings. Besides these there are 

 occasionally visible narrow belts in the northern and southern 

 temperate and polar regions. The two principal ones seem to 

 have kept their position ever since systematic observations 

 have been taken, but they are noticed to be constantly changing 

 in points of detail. The light equatorial band seems to be the 

 centre of the most intense forces, for the markings here are 

 constantly changing. I think it would be difficult in any series 

 of sketches to find the same detail twice on this part of the 

 planet. The general appearance remains fairly steady for some 



