It proves what I can’t see, that the earth at the equator is farther off the centre than what it is at London or Melbourne, and that would make the earth not a true Globe.
Neither is it my son: though the difference is but little. It is about a dozen miles thicker down to the centre at the Line than at the poles.
Then, as London and Melbourne are each nearly half-way between the line and the pole they will be nearer by six miles to the centre than the equator is.
You have solved the problem, and understand that the world is not a sphere, but what is called an Oblate Spheroid, being flattened at the poles.
As I cannot easily find out by weighing that a pound is not a pound: can you tell me any other way of proving that the earth is not quite round, dear father?
Yes, I can. Do you see the reason why the pendulum returns down when it is moved up?
The gravitation, to be sure.
If a thing weighs heavier in one place than another through a difference of gravitation will there be a difference in the two places with the pendulum?
I should fancy that where the earth pulled the harder the pendulum would come down the quicker.
If it came down quicker it would rise quicker; that is, the beat would be quicker. What effect would this have upon the clock?