Haroun is proud of himself for knowing enough mathematics to understand this on the first try!  "Why doesn't any pair of -"  He realizes his mistake a second later.  "Right, if something the size of a whole planet draws things downward at a rate slow enough to be livable, it'd take something the size of a mountain before you could notice any draw towards it at all!  And you'd probably just mistake it for a slightly different slope of the land, I mean, I can't think offhand of any standard measurement of 'downwards' except the direction gravity pulls.  If the mountain is pulling you towards it, it would just appear as the ground there being a little bit steeper!  You'd have to get a sextant and a clock and start calibrating by the location of the stars in order to get a different fix on directions than that!"

Haroun is proud of himself for knowing enough mathematics to understand this on the first try!  "Why doesn't any pair of -"  He realizes his mistake a second later.  "Right, if something the size of a whole planet draws things downward at a rate slow enough to be livable, it'd take something the size of a mountain before you could notice any draw towards it at all!  And you'd probably just mistake it for a slightly different slope of the land, I mean, I can't think offhand of any standard measurement of 'downwards' except the direction gravity pulls.  If the mountain is pulling you towards it, it would just appear as the ground there being a little less steep!  You'd have to get a sextant and a clock and start calibrating by the location of the stars in order to get a different fix on directions than that!"