Satellites of the Georgium Sidus , &c. 77 
render small stars and satellites invisible at so great a distance 
as 18 or 20". 
A dense atmosphere of the planet would account for the de- 
falcation of light sufficiently, were it not proved that the satellites 
are equally lost, whether they are in the nearest half of their 
orbits, or in that which is farthest from us. But, as a satellite 
cannot be eclipsed by an atmosphere that is behind it, a sur- 
mise of this kind cannot be entertained. Let us then turn our 
view to light itself, and see whether certain affections between 
bright and very bright objects, contrasted with others that 
take place between faint and very faint ones, will not explain 
the phenomena of vanishing satellites. 
The light of Jupiter or Saturn, for instance, on account of 
its brilliancy, is diffused, almost equally, over a space of several 
minutes all around these planets. Their satellites also, having 
a great share of brightness, and moving in a sphere that is 
strongly illuminated, cannot be much affected by their various 
distances from the planets. The case then is, that they have 
much light to lose, and comparatively lose but little. 
The Georgian planet, on the contrary, is very faint ; and the 
influence of its feeble light cannot extend far, with any degree 
of equality. This enables us to see the faintest objects, even 
when they are only a minute or two removed from it. The 
satellites of this planet are very nearly the dimmest objects that 
can be seen in the heavens ; so that they cannot bear any con- 
siderable diminution of their light, by a contrast with a more 
luminous object, without becoming invisible. If then the sphere 
of illumination of our new planet be limited to 18 or 20", we 
may fully account for the loss of the satellites when they come 
