Capital, capital

I've already linked to Bill Walsh's rant on why it's e-mail, not email. But we've never talked about why it's e-mail, not E-mail. There's a nice discussion going on at Testy Copy Editors that, while drawing no conclusions, is interesting to keep in mind when these tech stories force the next compound noun on us. (You'll have to scroll down a bit to ADKbrown's query.) My post:

In one of Bill's recent rants on why e-mail gets the hyphen, he points out that E is there as the letter E, not some E-sounding syllable. You don't see xray or aframe squashed together.

But in X-ray and A-frame, the caps are retained. So why isn't the E in e-mail?

I just looked up X-ray in my at-home dictionary, and it prefers the lowercase X for the verb (but not the noun). As for A-frame, that refers to the shape of a building like the letter A, not the like the lowercase a. (In the same category is T-shirt and T-top.)

O-ring also springs to mind. It's capped in my dictionary. And the shape of an O is the shape of an o, so why does it retain a cap?

But none of these are really parallel examples of words that have been truncated to one letter, like electronic to e. Can anyone think of something similar?

The short answer: There seems to be no rhyme or reason to which get the capped first letter. Dictionaries even differ on some entries: X-ray and C-section, for example.

Just one more reason that dictionaries are handy. Sometimes, there are no rules.