After studying (mainly BJTs, but with FETs in the final year) at Uni,
I was conversant with all the models, Hybrid-Pi, etc, and the use
of various matrical parameters, h, y, s, etc, for describing and predicting
transistor behaviour in circuit, but was puzzled on how it actually worked,
by which I mean, how did the base current control the collector current?

(So many of the textbooks just glibly say that the part of the emitter
current
divides off to become the base current, but this does not describe the
low-level controlling action)

I found the answer about 18 years ago in these NG (ISTR sci.electronics
before its unnecessary split), but I wonder whether anyone else puzzled
over this, and what was their answer?