Q:

"which" and "the more"

Newton postulated a law of universal gravitation according to which
  each body in the universe was attracted toward every other body by a
  force that was stronger the more massive the bodies and the closer
  they were to each other.

I have never seen "which" which is used after "according to." I've consulted a dictionary and reasoned that "which each body" means "every body." Is it right?
AND
I completely don't understand why the phrase, "the more massive the bodies" is right. I think it must be "the more massive body."
Tell me, please!

A:

The which in question refers to the law of universal gravitation. It could be rephrased as according to this law.
According to this law every body (object) in the universe is attracted towards every other body in the universe.
The force by which every body is attracted to every other body depends on two factors, the size of each body and its distance from every other body.
The more massive the bodies is correctly stated. It is saying that the force depends (partially) on the size of each and every body. The bigger they are, the greater the gravitational force that they exert. It would be wrong to say the more massive body.
In short, Newton had it right (at least until Einstein showed up).

