Euclid

yoo'klld, a famous Greek mathematician. He taught geometry in the noted school at Alexandria about 270 B. C. He wrote a work in thirteen books called the Elements of Geometry. Modern textbooks on the subject follow essentially the lines marked out by Euclid. His Elements without alteration might still serve as an excellent text. Many, in fact most, of his demonstrations, in point of brevity, clearness, and accuracy cannot be improved. In order to demonstrate the fallacy of perpetual motion devices, it is the practice in the United States patent office to cite the propositions of Euclid. No such device has ever been presented in an application for a patent which has not been disproved by reference to Euclid.