Thereupon this daring young man conceives the idea of inventing a system of astronomy himself, in which all the movements of the heavenly bodies should be shown to be in accordance with a simple and harmonious law. Seizing on this idea, he proceeds at once to develop it; and he works on it until death takes him from his labors in 1543 at the age of seventy. The whole civilized world had virtually accepted the Ptolemaic Theory,--at least, the part of it which assumed that the earth was the center of the universe, the sun and stars and planets revolving around it. Copernicus invented the theory that the sun was the center, that the earth and the other planets revolved around it, and that the earth revolved on its own axis once in twenty-four hours. So great was the insistence of the religious bodies in adhering to the Ptolemaic Theory, so set were the minds of all men of high position on it, that though Copernicus wrote a book expounding his own theory, he did not think it wise to publish it. He seems to have completed the book in about 1530. He did not publish it till 1543. Just before its printing was finished, Copernicus was taken ill. The first volume was held before him. He touched it and seemed to realize dimly what it was. Then he relapsed into torpor almost immediately, and soon died. It is interesting to note that Copernicus was not the first to conceive the idea that the earth turns on its own axis, or that the earth revolves around the sun, any more than Bell was the first to conceive the idea that speech could be transmitted by a suitable arrangement of magnet, diaphragm and electric circuit. But Copernicus was the first to invent a system of astronomy that was like a machine. It was a usable thing. It could be made to explain astronomical phenomena and predict astronomical events correctly. It may be well to remind ourselves again that no application for patent will be granted by our Patent Office unless the invention is described and illustrated so clearly and correctly that "a person skilled in the art can make and use it;" and to realize that this admirable phraseology may be utilized to distinguish any other novel endeavor of man entitled to be called an invention from any other not so entitled; for no system, no theory, no religion, no scheme of government, regardless of how attractive it may be, is entitled to be called an invention, unless, like the Copernican System, "a person skilled in the art can make and use it."