Star rises; from these two known truths an unknown thing has been discovered—that is, that the horizon is curved, meaning that the horizon of each degree of the earth is a different horizon from that of another degree. Man perceives this and proves from it an invisible thing which is the roundness of the earth. This it is impossible for the animal to perceive. In the same way, it cannot understand that the sun is the center and that the earth revolves around it. The animal is the captive of the senses and bound by them; all that is beyond the senses, the things that they do not control, the animal can never understand, although in the outer senses it is greater than man. Hence it is proved and verified that in man there is a power of discovery by which he is distinguished from the animals, and this is the spirit of man.