I have tried to bring together in a brief and compendious manner the various causes which produce greater moisture and a less degree of heat in America; it will of course be understood that the question respects the _general_ hygrometric state of the atmosphere, and the temperature of the New Continent as a _whole_. Single districts, such as the island of Margarita, the Coasts of Cumana and Coro, are as hot and as dry as any part of Africa. It must also be remarked that the maximum of heat at certain hours of a summer’s day has been found, on a series of years, to be almost equal at very different parts of the earth’s surface, on the Neva, the Senegal, the Ganges, and the Orinoco; being approximately between 27° and 32° Reaumur (93° and 104° Fahrenheit), and generally not higher,--providing the observation be made in the shade, at a distance from all solid bodies which could radiate heat to the thermometer, not in an air filled with hot particles of dust or sand, and not with spirit thermometers, which absorb the light. It is probably to fine grains of sand floating in the air, and forming centres of radiant heat, that we must ascribe the dreadful temperature of 40° to 44°.8 Reaumur (122° to 133° Fah.) in the shade, to which my unhappy friend Ritchie, who perished there, and Captain Lyon, were exposed for weeks in the Oasis of Mourzouk. The most remarkable instance of very high temperature, in an air probably free from dust, has been recorded by an observer who knew well how to place and to correct all his instruments with the greatest degree of accuracy. Rüppell found 37°.6 Reaumur, (110°.6 Fahrenheit,) at Ambukol in Abyssinia, with a clouded sky, strong south-west wind, and an approaching thunderstorm. The _mean_ annual temperature of the tropics, or of the proper climate of palms, is, on land, between 20°.5 and 23°.8 Reaumur (or 78°.2 and 85°.5 Fahrenheit) without any considerable difference between the observations collected in Senegal, Pondichery, and Surinam. (Humboldt, Mémoire sur les lignes isothermes, 1817, p. 54. Asie Centrale, T. iii. Mahlmann, Table iv.)