Whether to use Farther or Further.

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Away from the desk and all things computer for the moment, but keeping things going with scheduled blogs about the language we use. I hope you'll forgive me if I don't reply to any comments for the time being, but I'm having a well-earned (I think so) rest from work for a couple of weeks.
Whether to use Farther or Further. 
farther: more distant in space, time or degree. (these two have become more or less interchangeable, but 'further' is more often the choice when referring to degree).  'Charles Darwin's theories go much farther back in time than those of the Creationists.'
further: more distant, especially in degree, to a greater extent.  'Your arguments are specious and move you further from the truth.'