[Dixielandjazz] time signatures

[Jim Kashishian]

While driving between Seattle & Yakima, Washington recently (another
story!), my son & I were listening to the car radio.  A song came on that
was in 12/8 time, and I tried to explain the difference of the afterbeat
from 4/4 time, due to the triplets on each beat (subdividing 12/8 time), how
the afterbeat comes just a little later than in 4/4 time, etc.
 
Well, my son is a microbiologist, and my simple way of explaining this was
not good enough for him.  He wanted to know why this & why that.  I'm no
good whatsoever at explaining music to others, and although I got out the
pencil & paper later, I was not able to make it clear enough for him.  He
wanted the mathematical explanation.
 
Is there a book out there that explains time, musical time, that a
completely unknowledgeable person could begin to understand?
 
Jim