did not freeze over at that place. In the same season of 1780, Chesapeak Bay was solid, from its head to the mouth of Patowmac. At Annapolis, where it is 5¼ miles over between the nearest points of land, the ice was from 5 to 7 inches thick quite across, so that loaded carriages went over on it. Those, our extremes of heat and cold, of 6° and 98° were indeed very distressing to us, and were thought to put the extent of the human constitution to considerable trial. Yet a Siberian would have considered them as scarcely a sensible variation. At Jenniseitz, in that country, in latitude 58° 27′, we are told that the cold in 1735 sunk the mercury, by Fahrenheit's scale, to 126° below nothing; and the inhabitants of the same country use stove rooms two or three times a week, in which they stay two hours at a time, the atmosphere of which raises the mercury to 135° above nothing. Late experiments shew that the human body will exist in rooms heated to 140° of Reaumur, equal to 347° of Farenheit, and 135° above boiling water.[1] The hottest point of the 24 hours is about 4 o'clock, P. M., and the dawn of day the coldest.
- ↑ The following observations on heat and cold, as they affect the animal body, may
not be unacceptable to those who have not paid particular attention to the subject.
The living body, (not like the dead one, which assumes the temperature of the surrounding atmosphere,) maintains within itself a steady heat of about 96° of Fahrenheit's thermometer, varying little with the ordinary variations of the atmosphere. This heat is principally supplied by respiration. The vital air, or oxygen of the atmospheric fluid inhaled, is separated by the lungs from the azotic and carbonic parts, and is absorbed by them; the caloric is disengaged, diffused through the mass of the body, and absorbed from the skin by the external air coming into contact with it. If the external air is of a high temperature, it does not take up the superfluous heat of the body fast enough, and we complain of too much heat; if it is very cold, it absorbs the heat too fast, and produces the sensation of cold. To remedy this, we interpose a covering, which, acting as a strainer, lets less air come into contact with the body, and checks the escape of the vital heat. As the atmospheric air becomes colder, more or thicker coverings are used, till no more than the requisite portion of heat is conducted from the body. As it would be inconvenient in the day to be burthened with a mass of clothing entirely equivalent to great degrees of cold, we have resort to fires and warm rooms to correct the state of the atmosphere, as a supplement to our clothing. If we have not the opportunity, and the cold is excessive, the thinner parts, as the ear, the nose, the fingers and toes lose heat till they freeze, and, if the cold be sufficient, the whole body is reduced in heat, till death ensues: as sailors experience who escape from shipwreck, in Winter storms, on desert shores, where no fire can be found.
Of the substances we use for covering, linen seems the openest strainer for admission of air to the body, and the most copious conductor of heat from it; and is therefore considered as a cool clothing. Cotton obstructs still more the passage of both fluids, and wool more than cotton: it is called therefore a worse conductor of heat, and warmer clothing. Next to this are the furs, and the most impermeable of all for heat and air are feathers and down, and especially the down of the Eider duck.—(Anas mollissima.) Hence the insensibility to cold of the beasts with shaggy hair, or fine fur, and of the birds in proportion as they are provided with down and soft feathers: as the swan, goose and duck.
Among the substances which, as being bad conductors of heat, foment and warm the animal body, are the leaves of the Espeletia Frailexon, a plant newly discovered by the great naturalist and traveler Baron Humboldt, on the mountains of South America, at the height of 2,450 toises above the sea. These leaves being furnished abundantly with a soft down, restore immediately to their due warmth the hands, feet, or other members benumbed with cold; and collected as a bed, protect from death the Indian benighted in those regions of extreme cold. The same scientific traveler, by analysis of the air, at different heights on the mountain of Chimborazo which he ascended to the height of 3,036 toises, (546 toises higher than had ever been done by man before, and within 224 toises of its top) found that the oxygen being specifically heavier than the azotic part of the atmosphere, its proportion lessened in that ascent 27 or 28 to 19½ hundredth parts. The same circumstance had been before observed by Saussure, Pini and Rebout, on the high mountains of Europe, and must be among the principal causes of the degree in which the animal body is affected with cold in situations more or less elevated.
In addition to the effect of vital air, as the vehicle of animal heat, we may note that it is also the immediate cause, or primum mobile of life. For, entering by respiration into the air-cells of the lungs, divided from those of the blood but by a thin membrane, it infuses through that a stimulus into the blood, which, acting on the irritable fibres of the heart, excites mechanically the action and reaction of that muscle. By these the blood is propelled, and received again in a course of constant circulation and vital action communicated and maintained through all the system. Intercept vital air from the lungs, the action of the heart ceases for want of stimulus, the current of the blood, unaided, yields to the resistance of its channels, all the vital motions are suspended, and the body becomes an inanimated lump of matter.
