Manchester Memoirs, Vol. Iv. (1910), No. 1. 13 



fragmentary bodies again intersect each other at the 

 point of the planet's orbit where the explosion occurred. 



All the observations which I have made on the 

 evolution of the Jovian satellites and cometary ejecta, are 

 applicable alike to the Saturnian and other systems of 

 planetary satellites. The evidence of orderly progression 

 in the periodic times of the inner satellites of Saturn 

 differs in one respect from that indicated by the satellites 

 of Jupiter in similar positions, as the times of revolution 

 of the first and third satellites are in the ratio of i and 2, 

 and the times of the second and fourth are also in the 

 same ratio, as was first pointed out by Sir John Herschel.* 



Notwithstanding that the actual surface of Jupiter is 

 covered with dense vapours of great depth, just as the 

 terrestrial globe at one period of its history was enveloped 

 with an atmosphere of aqueous vapour which has since 

 condensed to form the oceans, several facts, in addition to 

 those advanced indicate that the Jovian planet has a 

 solid crust of considerable thickness. 



The remarkably bright round spots which suddenly 

 appear on the planet at irregular intervals, and have been 

 described by Lassell, and also by Dawes, as having some 

 resemblance to lunar craters,j- indicate considerable vol- 

 canic activity below the atmospheric envelope. The 

 eruptive matter from the Jovian craters also produces the 

 appearance of belts on his outer surface as well as those 

 seen on Saturn and Uranus. That these belts and bands 

 are caused by volcanic dust ejected to great heights from 

 the interior parts of planetary bodies is highly probable 

 from observations made on the great eruption of 

 Krakatoa in 1883.+ 



* " Outlines of Astronomy," p. 368, 1864. 



t Monthly Notices Roy. Ast. Soc, vol. 10, 1850; Ibid., vol. 18, 1857. 

 X " The Eruption of Krakatoa and Subsequent Phenomena." Report 

 of the Krakatoa Committee of the Royal Society, 1888. 



