to guard us against disease in bad air, or in an unwholesome country- The atmosphere that lies over the surface of the sea, as I have already said, is the purest; and this probably arises from the absorption of the mephitic particles by the mass of the waters. The air of the country is, in general, somewhat better than that of towns. Marshy grounds are, from their nature, unhealthy; and they are most so, when not cultivated. Good land even suffered to run waste, is injurious to man. Of this you have an instance in the Campagna, and in the environs of Rome. The insalubrity of the air, which is experienced in these parts, is in a great measure owing to the want of cultivation; and to the want of trees and vegetables, which would feed upon the bad, and return to the atmosphere a dephlogisticated air. This insalubrity, as you well know, is felt most in the summer, and in the night. During the day, the heat of the sun rarefies the air, and dissipates the mephitic exhalations. In the night,

the septic or putrid exhalations, indeed, continue; but they hover round the dwellings of men, for there is no heat to raise and to disperse them. Even those which had risen during the day, fall again upon the earth. All hot countries, that are low and damp, and not well cultivated,

VOL. I.

T

cultivated, are always unwholesome.

Dry', rocky, sandy countries, even without vegetation, are quite the contrary. If near the sea, so'much the better. Hence the healthiness of the situation of Gibraltar.*

But, here it may be asked, how these airs are concentrated, held, and ultimately set loose? The generation of airs is owing to the concentration of fire; for the airs are produced in that regular order, which is conformable to the quantity of fire they possess. For instance,

let us take the air from lime-stone. First, fixed air is expelled without any impregnation; next, phlogisticated air, with sufficient to neutralize the acid; then dephlogisticated air, with an higher impregnation; and at last inflammable air, which always varies with its substance, with the highest concentration. Vegetable bodies, indeed, as we have seen, are principally formed of the vegetable acid, with water and an earthy base, and these attract the fire of the sun, and concentrate it. When these again are exposed to the fire, the fire is attracted and concentrated likewise, and forms charcoal; and when the heat is pushed high, the concentration is so considerable, as to form inflammable air;

* Ingenhouz.

but

1

but if an over proportion of water enters, a proportionally less quantity of fire enters, and thus fixed air is formed. Hence it is also, that phlogiston and the nitrous acid form nitrous air; but, by adding a greater proportion of phlogiston to the air already generated, or before its generation, it will produce either inflammable or empyreal nitrous air. The same happens with regard to the vitriolic acid air. In the marine acid air, it is the same: by exposing it to iron, it will reduce the iron into a calx, seizing upon its phlogiston, and forming inflammable air. Every chymical process is a proof, that fire is chymically united with acids. When exposed to a strong heat, they become aerialized into phlogisticated, empyreal, or fixed airs.*

Swamps, morasses, and undrained and uncultivated lands, let me again repeat it, are fatal to the health and longevity of man. They send forth the seeds of pestilence and death upon the wings of every wind. They are the most certain, and the most durable calamity, that ever afflicted the human race. In every gale, the whole mass is tainted with putrescency, and teems with variety of life. The living at

mosphere, instead of the pabulum vita, becomes the indiscriminate dispenser of pain, sickness, and animal dissolution. In short, every thing becomes pestiferous. Of the effect in a smaller degree of corrupted air, a familiar instance occurs in cretins and goitres, which are chiefly found in those countries where there is a rank vegetation, and where the atmosphere is extremely humid, in consequence of numerous lakes, water-falls, and rivulets, which emit powerful exhalations through the influence of the sun's heat, while they are excluded from every drying wind. They, for example, who inhabit the deepest and most recluse vallies, are reduced to the lowest state of imbecility and idiotism. In those which are somewhat more elevated, the mental powers are not so completely obtunded; and others still more elevated, and exposed to fewer exhalations, and more salutary winds, will merely be deformed with wens and swellings about the joints. They who are nearer to the summits, are perfectly exempt from all these appearances. The inhabitants of more healthy vales may, indeed, become cretins, by residing in such unhealthy regions; but, it is at the same time more than conjectural, that the race of cretins may be meliorated, by transplanting them to a more salubrious soil. All

this you may observe among the Alps, or, as it more powerfully struck me, among the mountains of Stiria, Cerinthia, and Carniola. And if you still go further, you will find that direful scourge, the plague, propagated or destroyed by similar causes. At Constantinople, it prevails during the summer, and is greatly weakened, or entirely ceases, in the winter. In Egypt, on the contrary, it is most violent in winter, and infallibly ends in the month of June. This apparent contrariety, however, is to be explained on the same principle. The winter destroys the plague at Constantinople, because the cold there is very severe; and the summer revives it, because the heat is very humid, on account of the seas, forests, and adjoining mountains. In Egypt, the winter nourishes the plague, because it is mild and humid; but the summer destroys it, because it is hot and dry. It seems to act on it, as it does on the flesh of animals, which it does not suffer to corrupt.*

I would not willingly drop a word here, which in any respect might be liable to the construction of prejudice, or national partiality; but, I feel too strongly the impulse of truth, to withhold the remark, that it is a practice not always

T 3

⚫ Volney.