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instructing subject, and particularly useful to the invalid, we may just advert to the instruments by which the study may be facilitated. And for the improvement of which the public is considerably indebted to Mr. Leslie,

Prognostics of the Weather by the Barometer.

1. The mercury in the barometer rises during fair weather; it falls before rain, violent winds, or a heavy gale, and sinks still lower if the wind is accompanied by rain.

2. The barometer is highest during an east or north-east wind.

3. In frosty weather, the mercury ascends, and if it rises during open weather, frost may be expected; but if it ascends during rain, and continues to rise for two or three days, long fair weather may be expected. If it falls suddenly during fair weather, much rain generally follows.

4. The mercury remaining stationary, foretels a continuance of the same sort of weather.

5. When the mercury in the tube is concave on its surface, it is sinking; but when conver, it is rising.

6. When the mercury sinks a great space suddenly, it indicates a hurricane.

7. When the barometer is near the high extreme for the season of the year, there is little probability of immediate rain; but when it is low for the season, a fair day rarely occurs, the weather being heavy, and interrupted by sudden showers, with squalls of wind from the south-west, west, or north-west.

8. When the barometer is low, and the sky is promising for fair weather, a change of weather may soon be expected, but when it is high, very dark and dense clouds may pass over without bringing rain.

9. When the mercury rises much, and continues to ascend slowly, it foretels the continuance of fine weather; when it descends much but slowly, it indicates bad or unsettled weather.

10. When the barometer rises rapidly, it shews that the weather, whatever it be, will be of short duration; but when it sinks much, it prognosticates, that the weather will be durable.

11. The descent of the mercury, when the heat of the air is great, indicates thunder.

The Thermometer marks the absolute temperature of the atmosphere near its own situation, and is merely formed of an air-tight glass tube, placed on a graduated frame, and containing mercury, the minute expansions of which are readily seen.

12. If the thermometer rises in winter, it announces frost; if it then sinks somewhat, a thaw may be expected; and if it rise during the thaw, it predicts snow.

From observations taken by various persons, it appears, that in England, January is the coldest month in the year, and July and August, the

hottest; but, in all places above 60° of latitude, June is the hottest month. The temperature of April appears to be the mean temperature of the whole year, which is about 51°; the annual temperature of London, according to Dr. Kirwan, is 51° 9′. It rises during the space between March and June, 18°, or from 40" to 58° of the range of the thermometer. From June to September it rises near 7° higher, or from 58° to 65' nearly. But from this time the heat declines 6° 59′; between September and December it falls 18° 35′ more; and during winter, or from December to March, it declines 5.36°, or to 34-45° of the thermometer; but rises again to nearly 40°, which is the point from which we set out. According to Mr. Howard's calculations, the mean temperature of London is only 48°. He remarks that it varies as much as 4° in different years, these variations being periodical, and appear to recur in cycles of seventeen years. "The year 1816, he observes, was the coldest in the cycle of seventeen years, from 1799, which was of corresponding temperature." "The year 1806," he says, "" was the warmest of a cycle ;" and, according to his calculation, 1823 should have been the warmest of the cycle, which does not appear to have been verified. The air of London is two degrees warmer on the annual mean, than that of the country around it; this is occasioned by the multiplied reflection of the sun's rays from the houses; by the number of inhabitants and of animals, and the constant and large fires that are kept within it. But this excess of warmth in London over that of its vicinity is not perceived in the day, for it belongs exclusively to the nights, which are 3° warmer than the country. And it is a curious fact, that the atmosphere of London, during the day, is about the third of a degree colder than in the country, which Mr. Howard attributes to the interruption of a portion of the solar rays, by the thick smoky cloud that constantly veils the metropolis. The mean difference of temperature, however, between day and night, in London, is about 14° warmer for the days. The temperature of London, during the succession of seasons through the year, rises and falls 100°; that is, from its greatest heat, at 96°, to its greatest cold, at 5° below freezing.

The greatest heat ever known in England, was observed at Moffat, in August, 1764, when the thermometer stood at 116° in the sun; but at Lancaster, in 1757, the thermometer, by being placed in the reflection from a white-washed wall, rose to 150°.

The Hygrometer measures the dryness or dampness of the atmospheric air. Mr. Leslie's improved hygrometer is very philosophical in its construction, and efficient in practice; it consists of a simple differential thermometer,* with one of the balls covered by tissue paper, for the reception

* Mr. Leslie's differential thermometer consists of a long slender glass tube, terminated at each end by a globular ball, and beat somewhat into the form of the letter U. Each ball contains common air insulated in its own proper ball by the ARTS, No. 12. 2 D

of pure water when it is to be used. The degree of cold produced by the evaporation of the water marked by the descent of the liquid in the opposite stem) is directly proportioned to the dryness of the air, and continues to be so under all circumstances.

The Pyroscope, invented by Mr. Leslie, is an indicator of the heat of a fire. It is merely his differential thermometer, one ball of which has a covering of gold leaf. If placed before a fire, as the covered ball is not affected by the radiant heat, the action of it is marked by the expansion of air in the other. It therefore measures the radiant heat which the fire

gives off.

The Phytometer measures the quantity of light. It is a differential thermometer with one of the balls blown of black glass. The illuminating power of the air, and, therefore, the dulness or brightness of wea ther is shown by it. These qualities being occasioned by the relative quantity of indirect light, reflected from the sky. This instrument detects the slight alterations of temperature which this reflected light occasions.

The Ethrioscope is a pyroscope so varied as to be free from the influence of light and wind, during its employment. Its use is to measure the degrees of cold shot down from the upper atmosphere; which it does by being simply exposed under the open sky. In other words, it shows the comparative temperature of the upper strata of the atmosphere, as it refers to the lower strata.

The Atmometer, indicates the velocity of the wind. The evaporation of exposed fluids is in the direct ratio of the velocity of the air; therefore, as the atmometer consists of a porous earthenware ball, with a wide tube attached to it, if the tube be filled with warm water it will run into the ball, and then if two atmometers be used, one sheltered and the other exposed, or if an atmometer and hygrometer be used in conjunction, the two instruments will ascertain the velocity of the wind in a very accurate

manner.

The Rain Gauge and the Weather-Cock are also two very essential meteorological instruments, and by the means of these different contrivances, the heat, weight, and dryness of the atmosphere, may be measured; and the quantity of light which exists in it; the relative temperature of its upper and lower strata; the velocity and direction of the wind; and the quantity of rain which falls, may be ascertained.

intervention of a coloured fluid, which occupies a considerable portion of the connecting tube, and rises in some degree into one of the balls. The application of a certain degree of temperature to one only of these balls will, by contracting or expanding the included air, elevate or depress the coloured fluid in the opposite stem, and thus afford a measure for detecting very minute variations of temperature.

SECTION II.

OF BATHING.

Cold Bathing is an act of cleanliness; and is frequently resorted to to preserve health, as well as to restore it. But it is not to be resorted to indiscriminately; as in diseases of the contents of the belly and chest, it may be productive of mischief, and is highly improper during a costive state of the bowels. Properly had recourse to, it braces the whole system, and is particularly useful to young persons of relaxed fibre, especially to females. And, in general, the popular idea is a correct one, that the glow which succeeds the use of the cold bath, is a test of its utility; while, on the other hand, its producing chilliness, head-ache, and other uncomfortable sensations, is a proof of its being detrimental; for when cold water is applied to the surface of the body, caloric (that is the matter of heat) is carried off; and an effort is immediately made by the blood-vessels to supply the deficiency. An increased action, therefore, takes place in persons who are in health, or who are not too much debilitated, and a pleasant warmth is experienced; but should the body be too debilitated, this increased action does not take place; the blood is thrown in upon the internal cavities, congestion of the venous system of blood-vessels ensues; the heat that is lost cannot be re-supplied; and those symptoms are experienced which we shall presently more fully detail. According to Dr. Saunders, the general circumstances for which cold bathing appears to be of service, are, a languor of the circulation, accompanied with profuse sweating, and fatigue on moderate exertion; tremors in the limbs, and many of those symptoms usually denominated nervous; when the moving powers are weak, and the mind listless and indolent; but, at the same time, where no morbid obstruction, or visceral disease is present. Such a state of body is often the consequence of a long and debilitating sickness, or of a sedentary life, without using the requisite exercise to keep up the activity of the bodily powers. In all these cases, the great object to be fulfilled, is to produce a considerable re-action from the shock of cold water, at the expense of as little heat as possible. And when cold bathing does harm, it is precisely where the powers of the body are too languid to bring on re-action, and the chilling effects remain unopposed. When the patient feels the shock of immersion very severely, and from the experience of its pain, has acquired an insuperable dread of its application; when he has felt little or no friendly glow to succeed the first shock, but on coming out of the bath remains cold, shivering, sick at the stomach, oppressed with the head-ache, languid, drowsy, and listless, and averse to food and exercise during the whole day, we may be sure the bath has been too cold; the shock too severe; and no re-action produced at all adequate to the impression on the surface of the body. To avoid these evils, persons

should not remain too long in the water; and to excite the circulation, friction with a rough towel must be diligently employed: or

The Shower Bath may be had recourse to; which is an apparatus so contrived that the water falls through numerous apertures, from a cistern placed above the patient. It is of the same utility as the cold bath, and is often attended with peculiar advantages; for the sudden contact of the water in the common cold bath, is merely momentary, but, in the shower bath, may be prolonged, repeated, and modified, at pleasure; while the head and breast, which are exposed to some danger in the common bath, are here effectually secured by receiving the first shock of the water.

The Tepid Bath. The heat of the tepid bath ranges from about 86° to 97; that is, from the highest heat of the cold bath, to the lowest of the hot. It may often be used with safety and advantage, when the cold bath cannot; and is useful in ardent fevers, when the temperature of the body is a little above that of health, but the powers of it weak. In cutaneous diseases, it is often quite sufficient to produce relaxation of the skin, and a salutary glow of perspiration. The tepid bath, with friction, is a great restorative, and of singular service in rigidities of the joints.

The Hot Bath varies in heat from 97° to 100° of Fahrenheit; and has a peculiar tendency to bring on a state of repose, to alleviate any local irritation, and thereby induce sleep. The cases in which bathing is particularly called for, will be noticed under the different diseases that hereafter claim our attention; but we may here mention, that the hot bath is, upon the whole, a safer remedy than the cold, and is more particularly applicable to very weak and irritable constitutions, which the shock produced by cold immersion would overpower, and in which re-action could not be induced. Diseases of the chest; of the abdominal vicera generally; and those which seem to depend on an irregular action of the bowels: herpetic and other eruptions of the skin, are frequently removed by the hot bath. The cases in which it is likely to be attended with danger, are particularly those where there exists a tendency to determination of blood to the brain, and apoplexy has sometimes been produced by it-witness the death of Doctor Heber, Bishop of Calcutta. The lowest temperature will be required for eruptive diseases, and to bring on relaxation of the skin during febrile irritation. Paralytic affections require a warm temperature, and more heat should be employed for deep-seated diseases, than for those which are superficially placed.

The Vapour Bath is sometimes used in the place of the hot bath; and seems to produce greater relaxation; it is usefully employed in rheamatic gout, and inflammation of the abdominal viscera; of the kidneys, bladder, and uterus; in suppression of urine, and in spasmodic affections. Infants suffering from cramp, or other painful internal affections, are often wonderfully relieved by the hot or vapour bath. A simple and convenient vapour bath, may be formed of a common beer or spirit barrel, with a false

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