[Formendacil]

Mnemo is perfectly right about Tolkien's attitude towards "farther" and "further"--he makes a direct reference to this in one of his Letters--let me see if I can dig up the reference in the 23 minutes before class...

Aha! Here we are:

Originally Posted by 138, A Letter to Christopher Tolkien: 4 August 1953

The galleys are proving rather a bore! There seem such an endless lot of them ; and they have put me very much out of conceit with pans of the Great Work, which seems, I must confess, in print very long-winded in parts. But the printing is very good, as it ought to be from an almost faultless copy; except that the impertinent compositors have taken it upon themselves to correct, as they suppose, my spelling and grammar: altering throughout dwarves to dwarfs; elvish to elfish; further to farther; and worst of all, elven – to elfin. I let off my irritation in a snorter to A. and U. which produced a grovel.

--emphasis Tolkien's own

Originally Posted by 148, A Letter to Katherine Farrer: 7 August 1954

I am afraid there are still a number of 'misprints' in Vol. I! Including the one on p. 166. But nasturtians is deliberate, and represents a final triumph over the high-handed printers. Jarrold's appear to have a highly educated pedant as a chief proof-reader, and they started correcting my English without reference to me: elfin for elven; farther to further; try to say for try and say and so on. I was put to the trouble of proving to him his own ignorance, as well as rebuking his impertinence.

Again, italics are from The Letters, not me.

Originally Posted by 236, A Letter to Rayner Unwin: 30 December 1961

I suppose I should be grateful that Cox and Wyman have not inflicted the change from elven to elfin and further to farther on me which Jarrolds attempted, but Jarrolds were at least dealing with a MS. that had a good many casual errors in it.

Those are all the references I found in The Letters, but none of them match my mental memory of how Tolkien put it, but as my memory is hardly infallible and these quotes suffice, it is probably sufficient to post these and note that Tolkien was well aware that the 'proper' usage would be farther, and decided he did not wish to use it.