It is not the child Agassiz alone whom Nature thus invited; to the whole human race, in its childhood, its adolescence, its maturity, she has always been saying the same thing. She has been seeking, through all the ages, to disclose to us all the mysteries of this marvelous universe. We have been slow learners; it took her a great many centuries to get the simplest truths lodged in the human mind. The cave-dweller, the savage in his teepee, were able to receive but little of what she had to give. Yet before their eyes, every day, she spread all her wonders; with infinite patience she waited for the unfolding of their powers. All the marvels of steam, of electricity, of the camera, of the telescope, the microscope, the spectroscope, the Roentgen rays,--all the facts and forces with which science deals were there, in the hand of Mother Nature, waiting to be imparted to her child from the day when he first stood upright and faced the stars. Slowly he has been led on into a larger understanding of this wonderful universe. And what has he learned under this tuition? What are some of the great truths which have gradually impressed themselves upon his mind? He has been made sure, for one thing, that this is a universe; that all its forces are coherent; that the same laws are in operation in every part of it. The principles of mathematics are everywhere applicable; gravitation controls all the worlds and every particle of matter in every one of them, and the spectroscope assures us that the same chemical elements which constitute our world are found in the farthest star. "On every hand," says Walker, "we are assured that the guiding principle of Science is that of the uniformity of nature." It has also come to be understood that nature is all intelligible. Everything can be explained. This is the fundamental assumption of science. Many things have not yet been explained, but there is an explanation for everything; of that every thinker feels perfectly sure. "Fifty years ago," says Sir John Lubbock, "the Book of Nature was like some richly illuminated missal, written in an unknown tongue; of the true meaning little was known to us; indeed we scarcely realized that there was a meaning to decipher. Now glimpses of the truth are gradually revealing themselves; we perceive that there is a reason--and in many cases we know what that reason is--for every difference in form, in size, and in color, for every bone and feather, almost for every hair."[6] This is the latest word of the latest philosophy; there is a reason for everything. As Romanes says, Nature is instinct with reason; "tap her where you will, reason oozes out at every pore." If all things are rational and intelligible, then all things must be the product of a rational Intelligence. That conclusion seems inevitable.