Coincidently with this change of opinion as to the government of individual life, there came a change as respects the mechanical construction of the world. According to the Koran, the earth is a square plane, edged with vast mountains, which serve the double purpose of balancing it in its seat, and of sustaining the dome of the sky. Our devout admiration of the power and wisdom of God should be excited by the spectacle of this vast crystalline brittle expanse, which has been safely set in its position without so much as a crack or any other injury. Above the sky, and resting on it, is heaven, built in seven stories, the uppermost being the habitation of God, who, under the form of a gigantic man, sits on a throne, having on either side winged bulls, like those in the palaces of old Assyrian kings. THEY MEASURE THE EARTH. These ideas, which indeed are not peculiar to Mohammedanism, but are entertained by all men in a certain stage of their intellectual development as religious revelations, were very quickly exchanged by the more advanced Mohammedans for others scientifically correct. Yet, as has been the case in Christian countries, the advance was not made without resistance on the part of the defenders of revealed truth. Thus when Al-Mamun, having become acquainted with the globular form of the earth, gave orders to his mathematicians and astronomers to measure a degree of a great circle upon it, Takyuddin, one of the most celebrated doctors of divinity of that time, denounced the wicked khalif, declaring that God would assuredly punish him for presumptuously interrupting the devotions of the faithful by encouraging and diffusing a false and atheistical philosophy among them. Al-Mamun, however, persisted. On the shores of the Red Sea, in the plains of Shinar, by the aid of an astrolabe, the elevation of the pole above the horizon was determined at two stations on the same meridian, exactly one degree apart. The distance between the two stations was then measured, and found to be two hundred thousand Hashemite cubits; this gave for the entire circumference of the earth about twenty-four thousand of our miles, a determination not far from the truth. But, since the spherical form could not be positively asserted from one such measurement, the khalif caused another to be made near Cufa in Mesopotamia. His astronomers divided themselves into two parties, and, starting from a given point, each party measured an arc of one degree, the one northward, the other southward. Their result is given in cubits. If the cubit employed was that known as the royal cubit, the length of a degree was ascertained within one-third of a mile of its true value. From these measures the khalif concluded that the globular form was established.