Alberuni considers the Sun as the source of heat on the surface of the earth but he finds that this heat is not uniformly distributed. This uneven distribution of heat, according to Alberuni, is due to several reasons, one of them being the distance of proximity of the place to the equator.⁸¹ The equator receives the greatest amount of heat because there the Sun always shines overhead. The increase in distance from the equator means a decrease in the amount of heat and vice versa. The other important reason is the zenith distance at a given place, for zenith culmination produces an increase in heat.⁸² When the Sun is in the zenith of the southern hemisphere, this hemisphere would be much more heated but when it is in the zenith of the northern hemisphere the conditions would be quite the opposite. Another reason of the variation of temperature...