The only objection of any consequence, that has ever been made to the hypothesis of _climate_, is this, _that people under the same parallels are not exactly of the same colour_. But this is no objection in fact: for it does not follow that those countries, which are at an equal distance from the equator, should have their climates the same. Indeed nothing is more contrary to experience than this. Climate depends upon a variety of accidents. High mountains, in the neighbourhood of a place, make it cooler, by chilling the air that is carried over them by the winds. Large spreading succulent plants, if among the productions of the soil, have the same effect: they afford agreeable cooling shades, and a moist atmosphere from their continual exhalations, by which the ardour of the sun is considerably abated. While the soil, on the other hand, if of a sandy nature, retains the heat in an uncommon degree, and makes the summers considerably hotter than those which are found to exist in the same latitude, where the soil is different. To this proximity of what may be termed _burning sands_, and to the sulphurous and metallick particles, which are continually exhaling from the bowels of the earth, is ascribed the different degree of blackness, by which some _African_ nations are distinguishable from each other, though under the same parallels. To these observations we may add, that though the inhabitants of the same parallel are not exactly of the same hue, yet they differ only by shades of the same colour; or, to speak with more precision, that there are no two people, in such a situation, one of whom is white, and the other black. To sum up the whole--Suppose we were to take a common globe; to begin at the equator; to paint every country along the meridian line in succession from thence to the poles; and to paint them with the same colour which prevails in the respective inhabitants of each, we should see the black, with which we had been obliged to begin, insensibly changing to an olive, and the olive, through as many intermediate colours, to a white: and if, on the other hand, we should complete any one of the parallels according to the same plan, we should see a difference perhaps in the appearance of some of the countries through which it ran, though the difference would consist wholly in shades of the same colour. The argument therefore, which is brought against the hypothesis, is so far from being, an objection, that we shall consider it one of the first arguments in its favour: for if _climate_ has really an influence on the _mucous substance_ of the body, it is evident, that we must not only expect to see a gradation of colour in the inhabitants from the equator to the poles, but also different[085] shades of the same colour in the inhabitants of the same parallel.