difference of weight

A further problem with the chain model of the siphon is that siphons work by a gradient of hydrostatic pressure within the siphon, not by absolute differences of weight on either side.

But if the reason of differences of weight is not this, but rather the heaviness of earth and the lightness of fire, then some of the planes will be light and others heavy (which involves a similar distinction in the lines and the points); the earthplane, I mean, will be heavier than the fire-plane.