Hayy ibn Yaqzan: The Improvement of Human Reason

§ 1. Our Ancestors, of Happy Memory, tell us, that there is an Island in the Indian Ocean, situate under the Equinoctial, where Men come into the world spontaneously without the help of Father and Mother. This Island it seems, is blest with such a due Influence of the Sun, as to be the most temperate and perfect of all places in the Creation; tho’ it must be confess’d that such an Assertion is contrary to the Opinion of the most celebrated Philosophers and Physicians, who affirm that the fourth Climate is the most Temperate. Now if the reason which they give for this Assertion, viz. That these parts situate under the Equinoctial are not habitable; were drawn, from any Impediment from the Earth, ’tis allow’d that it would appear more probable; but if the reason be, because of the intense Heat (which is that which most of ’em assign) ’tis absolutely false, and the contrary is prov’d by undeniable demonstration. For ’tis demonstrated in Natural Philosophy, that there is no other cause of Heat than Motion, or else the Contact and Light of Hot Bodies. ’Tis also prov’d that the Sun, in it self, is not hot, nor partakes of any mix’d Quality: ’tis prov’d moreover, that the thickest and smoothest Bodies receive Light in the greatest degree of perfection; and next to them, the thicker which are not smooth, and those which are very thin receive no Light at all. (This was first demonstrated by Avicenna, never mention’d before by any of the Ancients.) From these Premises, this Consequence will necessarily follow, viz. That the Sun do’s not Communicate his Heat to the Earth, after the same manner as hot Bodies heat those other Bodies which are near them because the Sun is not hot in it self. Nor can it be said that the Earth is heated by Motion, because it stands still, and remains in the same posture, both when the Sun shines upon it, and when it does not, and yet ’tis evident to Sense, that there is a vast difference in it, in respect of Heat and Cold, at those several times. Nor does the Sun first heat the Air, and so the Earth; because we may observe in hot weather, that the Air which is nearest the Earth, is hotter by much than that which is higher and more remote. It remains therefore that the Sun has no other way of heating the Earth but by its Light, for Heat always follows Light, so that when its Beams are collected, as in Burning-Glasses for instance, it fires all before it. Now ’tis Demonstrated in Mathematicks, that the Sun is a Spherical Body, and so is the Earth; and that the Sun is much greater than the Earth; and that part of the Earth which is at all times illuminated by the Sun is above half of it; and that in that half which is illuminated, the Light is most intense in the midst; both because that part is the most remote from Darkness, which is the Circumference of the Circle, as also, because it lies opposite to more parts of the Sun: and that those parts which are nearest the Circumference of the Circle, have less Light; and so gradually, till the Circumference of the Circle, which encompasses the illuminated part of the Earth, ends in Darkness.