SECT. IV. Of the Qualities of the Air, and their Effects on Health.

THE qualities of the air depend on its being hot or cold, dry or moist, light or heavy, inland or maritime, breathed in the day, or in the night. It is well known what important effects these various circumstances produce on the health of the human body.

1. Hot Air.-The effects of hot air will be easily understood, if we consider for a moment, that the air either raises, or reduces to its own temperature, those bodies which it surrounds or penetrates *. When we see, indeed, after the colds of winter, how rapidly the heat of summer revives all nature, making the plants to grow, the trees to blossom, and every animal to rejoice, we cannot suppose that man should be the only exception. But its principal effects, in regard to the human species, result from this, that the quantity of perspiration, sensible and insensible, is, in a great measure, regulated by the degree of heat applied to the human bodyt. It is supposed that in England, at an average of the whole year, perspiration scarcely equals all the other excretions, though in summer it is nearly double to that of winter; whereas, in the air of Padua, during the whole year, the perspiration is supposed to be, to the other excretions, as five to three, and in tropical climates, it is probably still greater, especially to the natives of Europe.

Though the human body can bear considerable variations of temperature, yet the heat in the atmosphere, most congenial to the human frame, is from 50 to 70 of Fahrenheit. That temperature has generally prevailed in the countries most famed for intellectual exertion, and strength both of body and mind. When that proportion is much exceeded, the fibres are lengthened and relaxed, particularly in the young and growing 1, and hence proceeds the sensation of faintishness and debility in a hot days. It is believed that men cannot live long in an air much hotter than their own bodies, the average of which is calculated

Valangin on Diet, &c. p. 20.

↑ Arbuthnot on Air, p. 50. On that account, the children of Europeans should be sent from the East Indies to Europe, till their form and stamina are established.

To prove the effects of heat on animals, the celebrated Boerhaave put a sparrow and a dog into a sugar-baker's drying-room, where the air was heated to 146, or 34 beyond that of the human body. The sparrow died in two minutes, and the dog in twenty-eight. See Arbuthnot on Air, p. 46. The heat was calculated according to Hales's thermometer.

in children at 90°, and in adult persons at 98°*, though both will bear a more violent heat, for a short period of time.

When the air is extremely hot, by promoting perspiration, it dissipates the thinner, watery, and volatile parts of the blood, and by thickening that source of nourishment and life, lays a foundation for many disorders, more especially fevers, of a bilious, putrid, ardent, and malignant nature. Hence, an extremely hot climate is far from being wholesome.

2. Cold Air.-It is evident that cold must have effects on the human body, directly opposite to those of heat. Cold air braces the fibres, not only by its condensing quality, but by rendering the air drier. By bracing the fibres also, and more strongly condensing the fluids, it produces that strength and activity, which is so sensibly felt in clear frosty weather, when the cold is not too intenset. On the other hand, by contracting the fibres of the skin, and cooling the blood too much in those vessels which are most exposed to the air, some of the grosser parts, and most acrid or saline particles of the perspirable matter, which would evaporate in warm weather, are retained in cold, and produce coughs, scurvies, and other disorders to which cold countries are liable. It is strongly in their favour, however, that such regions are frequently affected by wind; hence the air is much more purified than in hot climates.

3. Moist Air. It has been well observed, that a little more or less of moisture in the air, can be of little importance to man, whose body is composed in a great degree of fluids, whose blood and juices are so watery, and who can swallow quantities of water and weak liquors daily, without inconvenience. Air, though moderately moist, therefore, can have no ill effect on the constitution, though, if it is saturated with moisture, it is unwholesome. Moist weather, indeed, even when accompanied by cold, is unfavourable to health, as is often fatally experienced by delicate people, during the fogs of London and Paris; but when it is accompanied by heat, it is still more prejudicial. Hence the great

The experiments of Blagden and his friends were made in rooms above the boiling temperature. A girl has gone into a baker's oven nearly 400°. † Cold air, in most people, also increases the appetite. It is remarkable, in the history of such as perished by cold in northern countries, that they kept their appetite to the last.-Arbuthnot on Air, p. 209.

Hippocrates, of old, observed that the Phasians were tall, soft, bloated and pale, on account of the excessive moisture of the air they breathed; their country being marshy, hot, watery, woody, and subject to violent showers, at all seasons.

mortality, during the hot season, at Batavia, and in some parts of America. When the air is impregnated with vapours from putrid marshes, it is found pernicious, not from its moisture, but its putridity.

4. Dry Air.-When the air is dry, it contains a number of saline and other particles, which, by rain or moisture, might have been carried down to the surface of the earth. It also imbibes animal and vegetable effluvia, which have a considerable influence on the body. By great dryness in the air, the very texture and situation of the pores of the skin may be altered. A dry air, if not too warm, is both agreeable and healthy, but when accompanied with great heat, is attended with the most fatal consequences, both to animals and vegetables*. Even in England it has been observed, that extremely dry seasons have been found more dangerous to human bodies than wett.

5. Light Air.-It is found by experience, that the lightness of air, on the tops of high mountains, is unfavourable to respiration. Persons in these elevated situations, are obliged to take breath oftener than in the lower regions; and are sometimes so violently affected, as to throw up blood, by the straining which the rarity of the atmosphere occasions. A certain portion of the pressure of the at

See the description of the Harmatan and the Sirocco, in Gregory's Economy of Nature, vol. i. p. 477, 478, &c. In Egypt, during a certain period of summer, the hot winds blow, called by the inhabitants campsin, from their continuance for fifty days, though they have no determined time, but last sometimes more than three months. The inhabitants, during the campsin, live much under ground.—Arbuthnot on Air.

Arbuthnot on Air, p. 183. Great droughts, he observes, have always been found noxious to the human body. Previous to the destructive epidemical distempers which took place in the latter end of the year 1732, and beginning of 1733, there was a great drought in England, and in the greatest part of Europe, which ultimately proved extremely fatal to all the places affected by it. Great droughts exert their effects after the surface of the earth is again opened by moisture, and the perspiration of the ground, which was long suppressed, is suddenly restored. It is probable that the earth then emits several new effluvia, hurtful to human bodies; and this appeared to be the case, by the thick and stinking fogs which succeeded the rain that had fallen before. See Arbuthnot on Air, p. 194, 199. Dr. Bisset remarks, that the inhabitants of places on the sea coast, are less subject to those diseases which generally result from an exceeding hot and dry summer, than those of inland towns.-Essay on the Medical Constitution of Great Britain, p. 3.—This is a circumstance much in favour of maritime situations.

Derham's Physico-Theology, vol. i. p. 11.

Lord Bacon (Nov. Organ. Scient. lib. 2, aphor. 12), says, when certain travellers mounted to the top of Olympus, the air was so thin that they were obliged to hold sponges, dipped in vinegar and water, to their noses and mouths. Also, that the air on the top of Teneriffe is so sharp as to

mosphere, being taken off the veins or blood-vessels, they expand and swell, by which a shortness of breath, and a spitting of blood are occasioned. When fermented liquors are carried in bottles to that height, the air contained in the liquor rarefies as much as the air without, by which means the bottles are burst. But though light air, when carried to an extreme, is so highly prejudicial, yet, in moderation, it may be of use; and hence the air of mountainous districts, is found to be of service in several disorders. In general, however, the air of lofty mountains is of too light and subtile a nature; and though it may be calculated for the eagle, and other descriptions of birds, yet it does not, in general, agree with the constitution of man.

6. Heavy Air.-Air in some measure compressed, or rather heavy, if it be dry, is not unfavourable to the human frame. It appears by authentic experiments, that animals live longer, when breathing a like quantity of compressed, than uncompressed air; and the weight of the atmosphere compresses the air in valleys and champaign countries, and consequently renders such air, better calculated to support great numbers of inhabitants*. It must also contain, for its bulk, a greater quantity of oxygen, or vital air†.

cause violent pains in the eyes; and so thin and light, as to make many vomit.

The air on one very high mountain of Peru, according to d'Acosta, is mortal at the first blast; and, by its coldness, dead bodies are preserved from putrefaction. At the top of one of these Peruvian mountains, which probably are the highest in the world, he and his company were seized with bilious vomitings, perhaps from the thinness as well as coldness of the air.-Arbuthnot on Air, p. 81.-But these assertions by d'Acosta seem to be greatly exaggerated. Humboldt has lately ascended one of the peaks of the Andes, more than 16,000 feet above the level of the sea. De Saussure, in his Voyages dans les Alpes," has given the best and most accurate account of highly rarified air, the effects of which he experienced, to their greatest extent, on Mont Blanc. They were exceedingly disagreeable, but not so pernicious as other travellers have described.

It is of great importance that the air should be of a due gravity and elasticity, that it may distend the lungs sufficiently; for however stronger constitutions can bear either an increased or diminished weight of the atmosphere, and can live on the tops of the highest mountains, or in the bottom of the lowest valleys, yet the sick, weak, and the valetudinary, cannot bear it-Short's Observations on Bills of Mortality, p. 420.

+ Dr. C. Harrison, of Horncastle, has found, that the air of the fens or marshes of Lincolnshire, is not favourable to the production of pulmonary consumption. Though that scourge of this island is reported to destroy annually such numbers of its inhabitants, yet in the fenny districts, it is rarely to be met with; whereas in the high-lying divisions of the county, (the wolds), where the air is less moist and bland, that disorder, originating in scrofula, is much more frequent. He further found, in a case or two of the kind which he adduces, that a removal from the high to the lower fenny part of the county, had repeatedly and uniformly the best effects.

7. Inland Air.-The air of inland districts must have qualities very different from those on the sea-coast. In the interior parts of a country, the air must partake much of the qualities of the soil and of its productions. Much, also, must depend upon the state of its cultivation. Even countries naturally unwholesome, if cleared of wood, and rendered fertile, become immediately healthy. It is also to be observed, that the central countries of great continents are colder, especially in winter, than those that have the seaair. Moscow, in the same latitude with Edinburgh, is much colder, during the winter months, though perhaps warmer in the summer season*.

8. Maritime Air.-The nature of the air at sea is, in various respects, very different from that which is to be met with in the inland parts of the country. 1. Sea air is more humid, owing to the great quantity of vapour which is constantly arising from the surface of such an extent of water. 2. The air at sea is more frequently agitated, and storms are more violent, and continue longer there than at landt. 3. In the same country, the air is found of very different temperatures, in regard to heat and cold, and possessing very different qualities; but, at sea, the air is more uniform, and less susceptible of variety. 4. The air at sea never stagnates, having no impediments to its course, from mountains, hills, or forests, and being continually agitated by the winds, currents, and the constant flux and reflux of the tides. 5. Sea-air is warmer, more especially in the extreme cold of winter, than the air which is incumbent on

Indeed wherever there is a spitting of blood, it is a sign that the situation of the place is too high, and the air too light. The proper plan to pursue, therefore, is, to fly to a flat or deep country, where the air is heavy. The weight of that sort of air must prevent the vessels from being swelled to any improper size: and the spitting of blood, which originated from the extension, must be removed.

Arbuthnot on Air, p. 78.

Strother, in his Essays on Sickness and Health, p. 26, contends, that the midland counties in England are the most healthy, and less subject to a variety of weather. He observes, that when the easterly or westerly winds give rains in abundance to the coasts, yet the middle way, between sea and sea, has then been calm and dry; the clouds brought from either sea, drop before they come mid-way. The accounts which are given of the air of Cheltenham seem to justify these observations.

+ In the British Encyclopedia, voce Aerology, p. 155, it is stated, that Dr. Dobson of Liverpool found sea-water contained air, superior in quality to that of the atmosphere. Hence the utility of sea voyages to invalids may arise. Arbuthnot, on the other hand, contends, that were it not for constant winds, which blow off the coat of vapours which invest the ocean, sea-air would be intolerable to human bodies.-On Air, p. 70.