Too much dryness or too much humidity are equally injurious to the duration of life; yet the air most favorable to longevity is that which contains a certain quantity of water in dissolution. Moist air being already partly saturated, absorbs less from the body, and does not consume it as soon as a dry atmosphere; it keeps the organs a longer time in a state of suppleness and vigor; while a dry atmosphere dries up the fibres and hastens the approach of old age. It is for this reason, doubtless, that islands and peninsulas have always been favorable to old age. Man lives longer there than in the same latitude upon continents. Islands and peninsulas, especially in warm climates, generally offer everything that contributes to a long life: purity of air, a moist atmosphere, a temperature often at one's choice, wholesome fruit, clear water, and a climate almost unvariable. I had an opportunity, long desired, of traversing the ocean as far the Tristan Islands, and of returning to the Indian Ocean by doubling the Cape of Good Hope with a captain who wished to observe the different islands on the way. I was thus able, in going as well as returning, to visit these numerous islands, and I can speak of them from reasonable observation. But it is sufficient to mention, from a hygienic point of view, the Isle of Bourbon, (where I lived for many years,) to give an idea of the sanitary condition of islands in general. Like most isles, the Isle of Bourbon has a form more or less pyramidal. The shore, almost on a level with the sea, is the part principally inhabited. There are few villages in the interior of the island, but many private residences. The temperature on the shore, though very high, is less intense than is supposed: the medium temperature being between 40° and 50°. The sea and land breezes, which succeed each other morning and evening, refresh the atmosphere and maintain a healthy moisture. It hardly ever rains except during the winter, Besides, it is very easy to choose the temperature one prefers. As the mountains are very lofty, they afford every season at once. On the summit are seen snow and ice, while at the foot the heat is tropical; so that it is sufficient to ascend for ten or fifteen minutes to find a marked change of temperature, And the colonists of but little wealth are careful to profit by this precious favor of nature. They select two or three habitations at different heights, in order to enjoy a continual spring, During the cool season, they reside on the sea-shore. Then they go to their dwelling a little above, where the temperature is mild. And in the hot season, they ascend to still higher regions.