Diseases prevail at the north pole as well as in the torrid zone; but those to which the Esquimaux, Greenlanders, and other northern tribes are subject, are for the most part different from those common between the tropics. Cold concentrates the vital spirits, strengthens the nerves, and causes heat, the proper vital power, to be accumulated in the interior parts; so that the body acquires a solid consistence, becomes strong and well-conditioned, and can bear all hardships without injury. It is attended, however, with this consequence, that it attracts the most dangerous diseases; creates violent, deep-rooted passions; blunts the judgement; and, if I may use the expression, involves it in dark clouds: though it cannot be denied that the mind thereby acquires a certain firmness, obtains dominion over itself, and is enabled to act with more caution. Heat, on the other hand, makes the body tender, and the nerves weak; gives more play to the human mind, and particularly the imagination; inflames the passions, and brings on diseases; but the former soon subside, and the latter are seldom dangerous. I shall not here examine whether the assertion, that mankind increase no-where so much as in cold countries, be well founded; but it is certain that they never thrive better than under a temperate climate. If the heat at the equator be scarcely supportable in the day-time, the nights, on the other hand, are more refreshing and pleasanter; and as they are equal to the days in length, the inhabitants are sufficiently indemnified for the oppression of the latter[226]. I cannot, therefore, agree with that French philosopher, who asserts that a six months residence at the north pole could be much easier endured than one of three at the equator, where, at certain hours of the day, the heat is moderated by a fresh cooling breeze. As long as the effects of nature do not contradict each other, so long will this principle be just, that men live much more agreeably under a mild climate, than in districts which are seldom visited by the benign influence of the sun. This is proved by many circumstances, and particularly by the emigrations of the Cimbri, the Huns, the Teutones, and the Marsi[227], who, leaving their unhospitable regions of the north, exposed to excessive cold, over-ran other countries lying more towards the south. The case was the same with the Turks, who, about the year 625, emerged from Scythia and Tartary; proceeded always further towards the east; and at length, after long and bloody wars, made themselves masters of Constantinople, in 1452. These, and other circumstances of the like kind, sufficiently confirm what I have said in regard to diversity of climate, and its influence on man.