Geoffrey Chaucer wrote his "Treatise on the Astrolabe" in 1387 for little Lewis, his to learn at Oxford. Manuscript copies of this work of Chaucer approaching completeness are very few in number and inaccessible to the general reader. He undoubtedly obtained the greater part of his book from Latin version of the Compositio et Operatio Astrolabii of Messahalla, an Arabian astronomer who is thought to have flourished about the end of the eighth century. Chaucer certainly was of opinion that he had achieved simplicity in his explanations, for he gave his Treatise the title of "Bread and Milk for Children."