Merriam-Webster Collegiate Dictionary - farther

 I. adverb  Etymology: Middle English ferther, alteration of further  Date: 14th century  1. at or to a greater distance or more advanced point got no ~ than the first page nothing could be ~ from the truth  2. to a greater degree or extent see to it that I do not have to act any ~ in the matter — Bernard DeVoto Usage:  Farther and further have been used more or less interchangeably throughout most of their history, but currently they are showing signs of diverging. As adverbs they continue to be used interchangeably whenever spatial, temporal, or metaphorical distance is involved. But where there is no notion of distance, further is used our techniques can be further refined. Further is also used as a sentence modifier further, the workshop participants were scarcely optimistic — L. B. Mayhew, but ~ is not. A polarizing process appears to be taking place in their adjective use. Farther is taking over the meaning of distance the ~ shore and further the meaning of addition needed no further invitation.  II. adjective  Date: 14th century  1. more distant ; remoter the ~ side of town  2. further 2 clearing his throat preparatory to ~ revelations — Edith Wharton