We cannot leave this subject without alluding again to the theoretical discussion of the influence of mountains on the climate of the polar regions that is found in that most interesting treatise of Robert Grosseteste, the _De natura locorum_. The bishop of Lincoln recognized the fact that insolation is greatly reduced in high latitudes owing to the obliquity of the sun’s rays and that the climate normally should be too cold to sustain life. He believed, however, that the presence of very high mountains, Rhipaean, Hyperborean, and others to which the authorities referred, might totally neutralize the effects of position in relation to the sun’s rays. “Some of these mountains,” he wrote,[809] “are smooth of surface, like the salt or rock hills that are found in many places, and others are in the nature of crystal, as divers authors and explorers testify, so that the reflection from them is good. As a result of this they are able to cause the rays all to converge and to produce a powerful effect. From these two accidental causes, that is from the smoothness of the mountains and from their concave shape, there is an intense heating of the air in certain regions around the pole. The great height of some of these mountains also cuts off the cold of the north, and thus certain localities may well be intensely hot.” On the other hand, Grosseteste had learned from Capella, Pliny, Solinus, and “many others who describe the regions of the world that in the Hyperborean Mountains next to the pole there are men who are called Hyperboreans from these mountains. And they enjoy the most temperate and healthy of climates and as a result live to such an age that they grow tired of life and without other cause throw themselves off of high rocks into the sea and die. The cause of this may be assigned to the form of the mountains beneath which they dwell, inasmuch as these mountains are smooth and of even surface, nor are they concave but are elongated (_oblongam_) and convex or of some other shape which does not concentrate the heat in those regions but on the contrary renders the climate temperate.”[810] INFLUENCE OF CLIMATE ON MAN In the literature of our period we find several observations about the influence of climate on man. Gervase of Tilbury[811] maintained that the character of the different European peoples varies with varying climatic conditions. “According to the diversities of the air the Romans are grave, the Greeks fickle and unreliable, the Africans sly and crafty, the Gauls fierce, and the English and Teutons powerful and robust.”