borne more directly upon its western shores, whereby its winters, but more especially those of this country, will enjoy a much higher temperature than formerly.

1286. Some of the causes tending to depress the mean annual temperature by exciting cold. "Elevation above the level of the sea; the vicinity of an eastern coast in high and middle latitudes; unbroken outline of a continent without deep sea bays; mountain chains whose form and direction prevent the access of warmer winds; extensive forests which hinder the sun's rays from reaching the ground, and whose leaves" absorb the sun's rays, and "throw off large quantities of watery vapour, and thus vastly increase the amount of radiating or cooling superficial surface; a misty or overcast summer sky, and a very clear winter's sky."

1287. The rate of mortality bears a tolerably close relation to temperature. More deaths occur during a low than during an elevated temperature, and during the colder than during the warmer months of the year.

1288. The following table, shewing the mortality of Scotland for the years 1855 and 1856, fully bears out this statement:-

1289. Night Air.-In this country the unwholesome character of the night air is attributed to its coldness. Dr. Wells says, "to our loss of heat by radiation is probably to be attributed a great part of the hurtful effects of the night air.” Descartes is of opinion that these are not owing to dew, but to the descent of certain noxious vapours, which, having been exhaled from the earth during the heat of the day, are afterwards condensed by the cold of the night. For this reason the practice of sleeping with open windows is highly dangerous, but more especially is this the case in malarious districts.

1290. It is generally admitted that in all countries the air is coldest about sunrise.

1291. Morning and evening mists formed on low ground are pernicious in their nature, from their holding miasmata in solution. When the former are dissipated by the morning sun, the latter are checked in their progress, possibly in their production.

"No one," says Dr. Macculloch, "fears a summer evening, or even a mild summer night, unless indeed he find a dew; yet here lies the very danger. A land of meadows, and parks, and ponds, and rivers, and woods is a thousand times more hazardous than all the nights of all the winters that ever were. This is the real night air to be feared, even tho' the grey mist should not rise, or the dew should not fall. To take a pleasant evening walk by the banks of the river or the lake, to watch the trout rise at the evening flies, to attend the milking of the cows in the green meadow, to saunter among wet groves until the moon rises, listening to the nightingale, these, and more of such rural amusements and delights, are the true night air, the malaria, and the fever."

1292. Soil.-"A gravelly soil," says Dr. Macculloch, "is healthy, because its easy drainage prevents the growth of that particular vegetation which is the cause of malaria."

1289. Op. cit. p. 251.

Meteorol. c. vi.

1293. Elevated gravelly sites are of necessity drier, and consequently more healthy, than low-lying gravelly soils.

1294. The gravel pits of commons, however, when filled with water, are a very general, and not less unsuspected, cause of ill-health.

1295. Dry and gravelly soils are exempt from typhus fever. 1296. Clay. "A clayey or marley soil is unhealthy, because, by permitting the accumulation and lodgement of superficial water, it generates, how partially soever, those marshy or undrained spots, or wet woods, or moist meadows, which are the sources of malaria, and, consequently, of the various diseases confounded under the vague term unhealthiness."

1297. Stone and sand have little capacity for caloric: they heat or cool, therefore, very rapidly, and to a great degree, and as readily, absorb or permit the percolation of water, which is again extricated by the solar rays in all the intensity and virulence of poisonous miasmata.

1298. The pestiferous nature of stone, limestone, and of sandy plains has been painfully illustrated (1000 to 1007) in the fearful loss which the British army sustained in the Peninsular campaign, and in the Walcheren expedition, when encamped on those soils.

and

1299. Chalk. If the chalk formation prove a very poor barren soil, of itself, it is, next to gravel, the most healthy of all soils. It very rapidly absorbs water, and as sparingly returns it to the atmosphere.

1300. The air of chalky soils is dry, tonic, and bracing.

1296. Op. cit. vol. i. p. 21.

CHAPTER VII.

CLIMATE AND DISEASE.

1301. In the preceding chapters we have considered the atmosphere, the seasons, temperature, rain, winds, pressure, respiration, circulation, infection, contagion, malaria, ventilation, and climate, and have, as amply as would appear necessary, discussed each subject in all its various bearings upon the sustentation of health, or production of disorder or disease. We have now only to enter upon the consideration of climate in the treatment, amelioration, arrest, or cure of functional derangement and organic disease.

1302. It must, however, be premised, that the conditions most favourable to health are an average degree of temperature, humidity, pressure, and electric tension, and that any departure from these conditions produces effects proportionate to the amount of such departure.

1303. If this be true in the matter of health, with how much greater force does it apply to disorder and disease.

1304. Invalids are exceedingly sensitive to changes of the weather. The fluctuations of temperature, humidity; and pressure affect their delicate organization in a manner and degree which few but themselves can estimate or comprehend, and which are only exceeded by the effect of the variations in the amount and kind of electricity in the atmosphere.

1305. Possibly it may be deemed not only not irrelevant to the subject under consideration, but even desirable, to refer, though briefly, to the climate of this country in particular, as well as to those causes on which climate more immediately depends, before proceeding to examine those of other countries

which have deservedly acquired celebrity as residences for invalids.

1306. The climate of this country, as a necessary consequence of the variable winds which blow in our latitudes, is exceedingly changeable; but, notwithstanding this variableness, the difference between the temperature of winter and summer *is, according to Mr. Glaisher, only 20·60°, and to Mr. Howard, 22.9°. (483.) For thus escaping the extremes of heat and cold we are indebted to the surrounding ocean, from which our winds derive their temperature. (1178.) Temperature, it has been already shewn, does not depend solely or entirely on the direct influence of the solar rays. To this small amount of variableness of the climate of our country its inhabitants owe the more robust health which they enjoy, and the greater longevity to which they attain, in comparison with those of the interior of large continents, Russia, for example, in which the difference between the average temperature of winter and summer is as great as 70° or 80°.

1307. The effects of temperature on the general health have been already adverted to (497), and reference has been made to the periodical return of "cold years" and "warm years," in connection with the recurrence of epidemic disorders. (379, 378.) This periodical invasion of disease is not, however, peculiar to our island; Livy tells us that in 173 years, i. e., from 287 to 460 A.C., nineteen distinct plagues occurred, none of them at longer intervals than seventeen years, and some continuing for two or three years together.

1308. The results of any departure from a due amount of humidity in the atmosphere have been already referred to. (518 to 525, 1269 to 1277.)

1309. A high state of the barometric column, as indicative of a dense condition of the atmosphere, is associated with epidemic disease. (634.) Diminished pressure is attended with increased cutaneous exhalation, and, if the fall be rapid, is accompanied with numerous sudden deaths. (640.)