Although the climate of San Juan is warm and damp, it is exempt from the fevers and epidemics which prevail in most places similarly situated, upon the shores of the Gulf of Mexico and Caribbean Sea. I could not learn that any cases of the yellow fever, or _vomito_, have ever occurred here; and when the cholera, in 1837, (five years after the period of its ravages in the United States,) devastated the interior, and almost depopulated the ports to the northward and southward, San Juan entirely escaped its visitations. It may safely be said that there are few ports, if any, under the tropics of equal salubrity. The nature of the soil, the fact that the malaria of the coast is constantly swept back by the north-east trades, and that good water may be obtained in abundance, at a depth of a few feet below the surface, no doubt contribute to this result. It is, however, a singular circumstance, vouched for by the older residents of San Juan, that the island or opposite shore of the harbor, not more than half a mile distant, and which, from the greater depth of water immediately fronting it, and other circumstances, seems to be the best site for a town, is fatal to those who may attempt to occupy it. A settlement was commenced there a number of years ago, but the inhabitants were decimated within the first two months; after which the rest removed to the other shore. The same cause, it is said, led to the abandonment of the military works which the Spaniards had erected there before the revolt of the colonies. The cause of this difference is not apparent, but no doubt as to the fact seems to exist among the inhabitants. Foreigners at San Juan, however, by observing ordinary and proper precautions, need not, I am convinced, form exceptions to the general good health of the native inhabitants. The temperature of San Juan varies a little with the different seasons of the year, but is generally pleasant, differing not much from that of New York in the month of July. The range of the thermometer is not, however, so great as it is with us during that month. During my stay in June, 1849, and upon my return in the same month, in 1850, the range was from 74° of Fahrenheit at sunrise, to 85° at the hottest hour of the day. In the evening there is usually a pleasant and invigorating sea-breeze.