This does assume that the two points are the same distance from the centre. Which is rarely the case given that planets aren't quite spheres. In fact, if you were to dig a tunnel from London to Lagos and drop something into the hole at the London end, I don't think it would ever reach Lagos. Instead it would get most of the way there and then go back to London.

IIRC this interesting little fact also assumes that the tunnel is straight - a tricky feat to pull off when most of the planet is hot and fluid.

In reply to Re^3: Where should one report search.cpan.org breakage? by DrHyde
in thread Where should one report search.cpan.org breakage? by frostman

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