On what grounds, then, does Mr. Buckle dispute the influence of religion? On two grounds mainly. First, he tells us that moral ideas are not susceptible of progress, and therefore cannot have exercised any perceptible influence on the progress of civilization. For that which does not change, he argues, cannot influence that which changes. That which has been known for thousands of years cannot be the cause of an event which took place for the first time only yesterday. "Since civilization is the product of moral and intellectual agencies," says Mr. Buckle, "and since that product is constantly changing, it cannot be regulated by the stationary agent; because when surrounding circumstances are unchanged, a stationary agent can produce only a stationary effect." On this principle, gravitation could not be the cause of the appearance of Donati's comet in the neighborhood of the sun. For gravitation is a stationary and uniform agent; it cannot therefore produce an accelerated motion. Mr. Buckle will answer, that though the law of gravitation is one and the same in all ages, and uniform in its action, the result of its action may be different at different times, according to the position in the universe of the object acted upon. True; and in like manner we may say, that, though religious ideas are immutable, the result of their action on the human mind may be different, according to the position of that mind in relation to them. The doctrine of one God, the Maker and Lord of all things, was not a new one, or one newly discovered in the seventh century. Yet when applied by Mohammed to the Arabian mind, it was like a spark coming in contact with gunpowder. Those wandering sons of the desert, unknown before in the affairs of the world, and a negative quantity in human history, sprang up a terrible power, capable of overrunning and conquering half the earth. Religion awakened them; religion organized them; religion directed them. The fact that an idea is an old one is no proof, therefore, that it may not suddenly begin to act with awful efficiency on civilization and the destiny of man.