| Re: mathementical/formal foundations of computing ? |
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Group: comp.lang.forth · Group Profile
Author: Jerry AvinsJerry Avins Date: Mar 6, 2007 13:40
John Doty wrote:
...
> But the role of theory in practice can get pretty tangled. Fleming and
> DeForest were both pretty good physicists, but neither understood what
> was going on in the vacuum tubes they invented. For them, theory seems
> to have inspired empirical investigation, but it didn't predict what the
> investigation would find.
Their vacuum tubes were based on the Edison effect, which is what
thermionic emission was first called. Edison discovered it as the cause
of premature burnout in light bulbs and learned how to suppress it by
using nitrogen fill do decrease an electron's mean free path. Once he
found how to sidestep its nuisance value, he stopped thinking about it.
Flemming and DeForest didn't ignore it. They knew about electron
emission because Edison told them. What they didn't know about was space
charge near the cathode. Geissler tubes were old hat by then, so
progress was fairly rapid. Space charge was discovered because electron
ballistics calculations that ignored it failed. It was an ad-hoc
fudge-factor fix that turns out to be real.
> Similarly, Brattain, Bardeen, and Shockley had a concept that we now
> call the field-effect transistor. Their theory was good as far as it
> went, but what they actually found in their experiments was the bipolar
> transistor. FETs require mastery of surface effects that were poorly
> understood in the 1940's.
The first field-effect transistors were built in the 30s, but they
weren't anything to write home about because zone melting to make pure
semiconductors hadn't been developed. Brattain, Bardeen, and Shockley
were the fine experimentalists who developed that. Their first result
wasn't a bipolar transistor, but point contact. Why? because that was an
easy extension of the cats-whisker crystal. The day that point-contact
transistors were announced to the lay world -- I read a description in
the New York Times on the subway ride to high school -- I made one for
myself. I used the pellet in a surplus 1N21B radar diode and two cat's
whiskers. I had a working oscillator before bed time. Knowledge is power
(fleapower in that case).
Jerry
--
Engineering is the art of making what you want from things you can get.
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