Note 40 — CHAP. I. AIR.

If the experiments of modern philosophy are to be depended on, they go a certain way to account for the unwholesomeness of air from woods in hot climates, and in wet weather; for Dr. Ingenhousz found that the effluvia of plants in the night time, and in the shade, are more poisonous in hot than in cold weather; but though there is a salubrity in the effluvia in sunshine, the heat of the weather makes no difference with regard to this. He found also that vegetables, when wet, yield an unwholesome air.

It is difficult to ascertain how far the influence of vapours from woods and marshes extend; but there is reason to think that it is to a very small distance. When the ships watered at Rock Fort, they found that if they anchored close to the shore, so as to smell the land air, the health of the men was affected; but upon removing two cables length, no inconvenience was perceived. I was informed of the following fact, in proof of the same, by the medical gentlemen who attended the army in Jamaica:—The garrison of Fort Augusta, which stands very near some marshes, to which it is to leeward when the land wind blows, was yet remarkably healthy; but it became at one time extremely sickly upon the breaking in of the sea in consequence of a high tide, whereby the water which was retained in the hollows of the fort produced a putrid moisture in the soil, exhaling a vapour offensive to the smell, and with all the noxious effects upon health commonly arising from the effluvia of marshes.