farther, further

Farther is used to refer to distance.
Further means "in addition," "additional," or "moreover." Need it be said that 'furthermore' is a stand in for 'moreover'?
In the interest of full disclosure, farther and further are often used interchangeably to refer to distance. I disagree. Associated Press has my back on this one.

"Any further comment from you, Napoleon, and we shall banish you to an island farther than Elba." --completely fabricated quote from 1814