This fact[083], of the variation of the mucous substance according to the situation of the place, has been clearly ascertained in the numerous anatomical experiments that have been made; in which, subjects of all nations have come under consideration.  The natives of many of the kingdoms and isles of Asia, are found to have their corpus mucosum black.  Those of Africa, situated near the line, of the same colour.  Those of the maritime parts of the same continent, of a dusky brown, nearly approaching to it; and the colour becomes lighter or darker in proportion as the distance from the equator is either greater or less.  The Europeans are the fairest inhabitants of the world.  Those situated in the most southern regions of Europe, have in their corpus mucosum a tinge of the dark hue of their African neighbours:  hence the epidemick complexion, prevalent among them, is nearly of the colour of the pickled Spanish olive; while in this country, and those situated nearer the north pole, it appears to be nearly, if not absolutely, white.

These are facts[084], which anatomy has established; and we acknowledge them to be such, that we cannot divest ourselves of the idea, that climate has a considerable share in producing a difference of colour.  Others, we know, have invented other hypotheses, but all of them have been instantly refuted, as unable to explain the difficulties for which they were advanced, and as absolutely contrary to fact:  and the inventors themselves have been obliged, almost as soon as they have proposed them, to acknowledge them deficient.

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