A glass ball is a massive sphere made of glass. You should be aware that solid objects are conceptual things. If you clip away parts of the sphere you'll clearly see that the interior is empty and it just has a very thin surface. This is not contrary to the concept of a solid object used in POV-Ray. It is assumed that all space inside the sphere is covered by the sphere's interior .
Light passing through the object is affected by attenuation and refraction properties.
However there is no room for any other particles like those used by fog or interior media. The object's interior is empty, it normally contains air molecules. An empty object can be filled with particles by adding fog or atmospheric media to the scene or by adding an interior media to the object. It is very important to understand that in order to fill an object with any kind of particles it first has to be made hollow. In order to be able to put solid objects inside a media or fog, a test has to be made for every ray that passes through the media.