I was thinking that the abbreviation for the element silver was “Ar,” see, and I had figured out this great, stupid joke I was going to bestow on the world. It was going to go like this:
“Hey, Long John Silver, how do you abbreviate your last name?”
“Ar.”
Because he’s a pirate — get it? Get it?
Yeah, it turns out the abbreviation for silver is “Ag.” Which means that my stupid geek joke doesn’t even work as a stupid geek joke, and I’m left trying to think of some reference to something like “Agamemnon” that isn’t funny even by my own abysmally low standards, and the Internet has been deprived of this crumb of humor it so desperately needed.
This has been a fruitless and un-insightful look directly inside my brain. You’re welcome.
Brian D. Buckley 
There might be a metaphor about him being vital to keep the main element of the book going (he is a father figure and teacher to Jim) and argon (Ar) being used in lightbulbs to stop the element burning out.
Ar.