Now by a _law of nature_ is meant any regular, or uniform action which we observe in nature. For example, it is called a law, or rule of nature that (with certain exceptions) heat should expand bodies, which merely means that we see that it does so. In other words, we observe that heat is followed by expansion, and we therefore assume that the one is the cause of the other. But calling it a law of nature for heat to expand bodies, does not in any way account for its doing so. And the same is true in other cases, so that a law of nature _explains_ nothing, it is merely a summary of the facts to be explained. It should also be noticed that a law of nature _effects_ nothing. It has no coercive, or compelling power whatever. The law of gravitation, for instance, has never moved a planet, any more than the rules of navigation have steered a ship. In each case it is some power or force acting according to law which does it. And _natural forces_ are those which, as far as we know, _always_ act according to some fixed law. They have no freedom of choice, they cannot act or not as they like; they must always and everywhere act the same under the same circumstances. We pass on now to the subject of Evolution, first considering its meaning, and then its effect on the present argument. (1.) _The meaning of Evolution._ Now by the term Evolution is meant to be included the processes of Organic Evolution, Natural Selection, and the Survival of the Fittest. The former may be described as meaning that all the different forms of life now existing, or that ever have existed on this earth, are the descendants of earlier and less developed forms, and those again of simpler ones; and so on, till we get back to the earliest form of life, whatever that may have been. And the theories of _Natural Selection_ and _the Survival of the Fittest_ explain how this may have taken place. For among the slight modifications that would most likely occur in every organism, those, and only those, would be perpetuated which were of advantage to it in the struggle for existence. And they would in time, it is assumed, become hereditary in its descendants, and thus higher forms of life would be gradually produced. And the value of these theories is that they show how Organic Evolution may have taken place without involving any sudden change, such as a monkey giving birth to a man. We must remember, however, that the subject is far from settled; and even now naturalists are beginning to doubt whether all the modifications were in reality very slight. But still, speaking broadly, this is the theory we have to discuss.