Gravity is not serious studied as yet, but it does appear that the force of gravity is not as strong in the Obscure World as in ours. We do know that the planet on which rests the Continent is a little smaller than our own. A lesser gravity would explain in part how Obscure people can build so tall and fly in machines equipped with propellers so small. This state of affair may possibly have come into being following the disappearance of Taxandria. In the Hollow Earths system, which has a special affinity with the Obscure Cities, gravity follows very different rules than those to which we are accustomed 1).