D. Trowbridge on the Nebular Hypothesis. 39 
tothe extremity of the system. ‘The Earth has 1, Jupiter 
Saturn 8, Uranus 6 and perhaps 8, Neptune 2 that have probably 
been seen. We cannot tell with certainty the number of satel- 
lites belonging to each of the last two planets, owing to the dif- 
ficulty of observing such bodies at so remote distances. The 
satellites of Jupiter are distributed in the Jovian system very 
similarly to the primary planets in the Solar System. We fin 
the masses to increase as the distance from the center of Jupiter 
increases, till we arrive at the third satellite, where we reach the 
aximum. ‘The fourth satellite is the second in mass. The 
third satellite is also the largest, and the fourth the next in size, 
but the second, although it is of greater mass, yet is of smaller 
size than the first. The satellites of Saturn follow a similar 
Uranus. We may therefore conclude that the outer planets had 
to condense much more than the inner ones before a satellite- 
tion of the rotation of the primaries. 
_ 57. The rings of Saturn offer a li | 
tive secondary rings. They open to us, in & measure, the nature 
to Prof. Peirce, by the attraction of the satellites. Should these 
tings entirely break up, they would probably form asteroid sat- 
ell ince the rings of Saturn are very thin In comparison 
with their width, we conclude that the primitive planet was very 
