 We know, say, that a clump of dirt has certain qualities such as extension and mobility, but how do we know that the entire earth has such qualities? It surely lies beyond the reach of our experiments, or at any rate, it did in Newton’s day. Newton says that the sun and the earth interact according to his law of gravity, but how do we know that the sun contains a quantity of matter, that it is a material body with the same basic qualities that characterize the earth or the moon? It wasn’t at all obvious at the time that the sun is a material body at all. Newton thinks that gravity reaches into the very center of the sun, but what did anyone in 1713 know about such things? Newton glosses his third rule in part as follows, connecting it with his laws of motion: