In a message dated 14-Jul-99 16:11:29 Eastern Daylight Time, lherault@bu.edu
writes:
> I'm guessing Pos. earth had something to do with electrical practice current
> (no pun intended) when automobiles were being developed.
<< snip >>
You got it - the early engineers guessed wrong in the 19th Century. They
theorized that electrical "current" flows from positive to negative. Those
early engineers were using a water analogy ( water flowing from a higher (+ =
positive, more water) to a lower (- =negative) level).
Nels Bohr didn't describe atomic structure until the early 1900's. Only
after that (and DeForest's invention of the vacuum tube) did the fact that
negatively charged electrons flow to the positive become known. But it takes
a while to change how we look at things. (Witness the US reluctance to go
Metric.)
In the late 50's, when I was working for AT&T, we had a basic
electrical/telephony course for us newbies, who were in our teens. The
instructors had a hell of a time switching to "electron flow" during the
course. They had grown up on "current flow." The impetus for the switch
had to do with the introduction of the transistor. Vacuum tubes (called
valves by the Brits - showing the water analogy) had first caused the problem
but those old timers (who were teaching us) had kept with the "current flow"
theory. Problem was that electrons flow from the negative side to the
positive side and "current flow" breaks down when explaining circuits with
vacuum tubes (or transistors). By the late '50's it was realized that it was
too much trouble to keep using "current flow." So the EE's ( and the AT&T
course designers) began the switch to "electron flow."
The early automakers grounded the positive side because they thought that the
gounded side needed a greater "potential" (meaning more potential charge to
them) hence that was available from the "earth" (or body in the case of
cars). Think about it - "It's all very logical, Cap'un."
BTW I've been sitting here for several days biting my tongue -- we had a
thread on this about 2 years ago and beat it to death then. Cheers.
Art Kelly
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