Alexander von Humboldt gives the law determining these facts in the following passage (_Asie centrale_, vol. iii, p. 23): “The foundation of the science of climatology is the accurate knowledge of the inequalities of a continent’s surface (hypsometry). Without this knowledge we are apt to attribute to elevation what is really the effect of other causes, acting, in low-lying regions, on a surface of which the curve is continuous with that of the sea, along the isothermic lines (i.e. lines along which the temperature is the same).” By calling attention to the multiplicity of influences acting on the temperature of any given geographical point, Von Humboldt shows how very different conditions of climate may exist in places that are quite near each other, independently of their height above sea-level. Thus in the north-east of Ireland, on the Glenarn coast, there is a region, on the same parallel of latitude as Königsberg in Prussia, which produces myrtles growing in the open air quite as vigorously as in Portugal; this region is in striking contrast with those round it. “There are hardly any frosts in winter, and the heat in summer is not enough to ripen the grapes.... The pools and small lakes of the Faroe Islands are not frozen over during the winter, in spite of the latitude (62°).... In England, on the Devonshire coast, the myrtle, the camelia iaponica, the fuchsia coccinea, and the Boddleya globosa flourish in the open, unsheltered, throughout the winter.... At Salcombe the winters are so mild that orange-trees have been seen, with fruit on them, sheltered by a wall and protected merely by screens” (pp. 147–48). Footnote 93: I will explain in due course the reasons why I do not include the American Indian as a pure and primitive type. I have already given indications of my view on p. 112. Here I merely subscribe to the opinion of Flourens, who also recognizes only three great subdivisions of the species—those of Europe, Asia, and Africa. The names call for criticism but the divisions are in the main correct. Footnote 94: