The Allegory of the Cave. The dialogue between Socrates and Glaucon is probably fictitious and composed by Plato; whether or not the allegory originated with Socrates, or if Plato is using his mentor as a stand-in for his own idea, is unclear. In the dialogue, Socrates asks Glaucon to imagine a cave, in which prisoners are kept.
The d sublevel consists of five orbitals that can hold a maximum of  two electrons each. The total maximum number of electrons that the  d sublevel can hold is 10 electrons.
An outermost shell has no more than 8 electrons (2 in the s orbital and 6 in the three p orbitals) because after the s and p subshells are full, adding another electron will start filling the s subshell of the next shell farther out, which then becomes the outermost shell. http://en.wikipedia.org/wiki/Auf...