Now, the moment we bring heat to bear on the body we find its surface moving in the outward direction. The whole mass is clearly under the influence of some suction which is directed on to the body from outside. Just as the plants grow in the anti-gravitational direction as a result of the suctional effect of levity (other factors which account for its growing into a particular shape, etc., being left out of consideration), so our copper ball grows in volume by being sucked away from its centre of gravity. It is the action of heat which has changed the ratio between gravity and levity at this spot in such a way as to allow levity to produce this effect.⁵