In your original post, you said: "it is not clear to me
what other role 'the farther' plays besides its role as an adverb."
I replied: Farther
and less are simply adverbs.
And you then said: "I want to know if the usage of 'the
farther' in this sentence is a well-known grammatical construction."
And I replied: "The two clauses are linked by the …
the …, which function as correlative conjunctions comparable to such pairs
as either/or, neither/nor, etc." Correlative conjunctions are a
well-known grammatical construction. In a subsequent posting, I explained that one of the
correlatives is omitted but understood in the original sentence.
All the grammatical functions having been accounted for, I
am puzzled. Exactly what part of your question remains unanswered?