The point I was trying to get across is that the tides are an ineraction between the strength of gravity of the moon and the centrifugal force (or inertia) of the different parts of the Earth.

At the bottem of page 68 the book says:

It seems paradoxical that gravity can act in such away as make something feel a force away from an object, but in this case it's because we are measuring the force relative to the centre of the Earth. When you do that, then you do indeed get a force pointing away from the moon on the far side of the Earth.

This is simple wrong the gravitational force does only act towards the moon and it doesn't matter where you measure it relative to. The force which pushs the far side out is the centrifugal force (or inertia) which is not mentioned until the effect of the Sun is included, were it says that the tides are due to the effect of both centrifugal forces and gravity.

The point I was trying to make with the force always acting towards the centre of mass was that it always acts 'downwards' and was not able to push things apart, (Well at least on the scales we are talking about I am aware that some cosmologists are suggesting that the cosmological constant should be reintroduced) rather than define the exact direction of the force.

I hope I clarified my point and now I can get back to reading the rest of the very enjoyable book.

Simon