Well, I've never heard even an American say, "farthermore" or "farther to our discussion". Although I have heard "further" used for distance, as if it's interchangeable with farther. But that doesn't make it right.Farther is American. Further is British. (Point me to the dictionary entry that says something else.)
http://dictionary.reference.com/search?q=fartherFarther is American. Further is British. (Point me to the dictionary entry that says something else.)
far·ther or fur·ther, far·thest or fur·thest. –adverb 1.at or to a great distance; a long way off; at or to a remote point: We sailed far ahead of the fleet.
Do you mean that Americans are simply more likely to use further for distance? Or are you saying that Americans always use further for distance to the exclusion of the word farther? Because I don't believe that's a correct statement.Farther is American. Further is British. (Point me to the dictionary entry that says something else.)
Do you mean that Americans are simply more likely to use further for distance?
Usage Note: Since the Middle English period many writers have used farther and further interchangeably. According to a relatively recent rule, however, farther should be reserved for physical distance and further for nonphysical, metaphorical advancement. Thus 74 percent of the Usage Panel prefers farther in the sentence If you are planning to drive any farther than Ukiah, you'd better carry chains, and 64 percent prefers further in the sentence We won't be able to answer these questions until we are further along in our research. In many cases, however, the distinction is not easy to draw. If we speak of a statement that is far from the truth, for example, we should also allow the use of farther in a sentence such as Nothing could be farther from the truth. But Nothing could be further from the truth is so well established as to seem a fixed expression.
Farther is American. Further is British. (Point me to the dictionary entry that says something else.)
I also pronounce it as further for both meanings... someone that pronounced it as farther would sound a bit odd in this area. It doesn't match the local accent.
So I wouldn't discount the idea of regional variation.