The man of science, when he is endeavoring to discover whether some thing or quality of a thing really existed at some time in the past, is not in the least concerned to establish the fact that some one saw it.

No one ever saw the primitive fire-mist from which, as we are told, the world came into being.

But the scientist cares little for that.

He is concerned only to prove that the phenomena he is investigating really have a place in the objective order.

If he decides that they have, he is satisfied; he has proved something to exist.