More and more writers these days think “further” is the same as “farther.” The words are not the same. They differ in physics.
“Farther” is space; “further” is time. Simple.
Two days ago I saw on the back of a tractor-trailer an easy way to explain the difference, though not as simple as farther-space and further-time.
The small sign on the back of the trailer asked: “How far did you go today?” And then: “Would you like to go …”
Which: farther or further?
If “further,” then the first statement would have to read: “How fur did you go today.”
If “further” is distance, then “fur” is proper application of “How fur is it?”
But, “further” is not distance.
“Would you like to go farther?”
Now, go ye forth and know the difference.
Don’t even get me started on “supposebly.” I will scream and apply forever curses.