seems probable that the atmospheric changes of the hour are also in accordance with perfectly definite results of the celestial motions. That is, if we may use a nautical expression, it is not probable that the weather at any and every point of the earth, at a particular moment, is a result of a daily special arbitrament of the Supreme Providence, (communicated to a clerk of the weather,) but that it results from laws as certain and predeterminate as those of the planetary motions.

The climate of the earth is then a result of its relation to the sun's light, and is determined by the globe's motion in accordance with gravitation, the vibrations of the atmosphere, and the grand pauseless mechanism of the heavens.

Independent of all the regular irregularities which the constantly changing gravitation of the other planets of our system inevitably produces in our atmosphere, a slow but certain change of climate must demonstrably result from the earth's course in the procession of the equinox-this is equal to 23 degrees of latitude, and is further illustrated by the zone of tropical fossils, palms and culmiferæ, elephants and mastodons, which is found to encircle the middle latitudes and the ices of Siberia. The very clouds which, borne on the changeful winds, are reflecting light and shadow on the earth at this moment, are doubtless a result of the equipoise of the earth's atmosphere, adjusted like the eclipses, and the subsidence of the geological formations to the laws of gravity acting during interminable ages.

This slow progression of the equinoxes carries with it, round the zones of the earth, a change of climate equal to forty-seven degrees of latitude, and thus, as plants and animals of a given species are generally capable of vigorous existence only within certain relations to the sun's light, and really inhabit only narrow zones of earth's landscapes, as

the sun's light and climate alter, so must the prevailing vegetables and animals advance or recede, taking place of those which may be stunted or dispossessed by the altered temperatures; thus an immense and constant succession is taking place, so that the change of the earth's poles, we state as an imaginary illustration of the probable effect of subjecting the Caucasian races of the temperate zones to the arctic or tropical temperatures, is in fact, to a considerable extent, a variation of real occurrence once in a thousand ages, i. e. an equinoctial cycle.

The real miracle of nature surpasses the dreams of the mythologists. It may well be said "the undevout astronomer is mad." The miracle of reality transcends the elaborate and incredible fables of the Pagan nations. As we study the true and demonstrable grandeur of Creation and the Creator, we shall be content to dispense with many of those miracles of past ages, in which the veneration and prolific intellect of the ancient nations, during its long struggle toward the goal of reality, compensated itself for those clearer illuminations and dispensations of the Supreme Wisdom, which appear to be slowly dawning on the advancing vista of future generations.

CHAPTER VIII.

The Influence of Climate on Animal and Vegetable Life.

The subject of this chapter-the influence of climate upon animal life, upon the means of maintaining health and the causes and characteristics of disease in all climatespresents considerations of great utility, variety and interest.

Our method of illustration is designed to portray the entire range of climate as it exists at the same moment, from the extreme limit of human habitations thinly scattered upon shores where the currents of the tropical ocean make the deepest impression upon the vast inhospitable ices of the poles, to those latitudes where a thousand species of palm-trees are lifting themselves in the heavens,—and where man lives almost without labor upon the spontaneous fruits which nature offers him beneath the fervid heat of the vertical sun.

The effects of temperature on man throughout the whole range of his habitations are incessant and resistless. From the earliest to the latest moment of life they are continually modifying the physical condition and the intellectual action of every human being, whether in health or disease.

Dr. Edwards, one of the latest and most approved of medical writers, says, "There is scarcely any agent which exerts a more powerful influence on life than the temperature of the atmosphere; hence its relations are amongst those which it is the most important to know. There is, moreover, no agent which we have more in our power to modify and adapt to our necessities. When circumstances prevent our doing so, as when we are exposed to the open air-[he probably was writing by a good warm fire,]—we have other resources to supply the deficiency. Hither to our care in this respect has merely been guided by instinct, or by that kind of observation which every body can make. But it requires a more intimate knowledge of our relation to the external temperature, properly to regulate the employment of means expedient to protect us from the injurious influence of heat and cold."

Nothing is more common than for persons to be injuriously affected by changes of temperature, in other words, to take cold; and yet they seldom know how or where they have taken cold, or cold has taken them. Dr. Ed

wards' chapter on this subject is worthy of a careful reading. It is chiefly devoted to the capacity of animals to sustain cold at different periods of life. It is not in our power to do more than to advert to one of his conclusions, which is, no doubt, just: "that the young of all animals suffer less and recover more perfectly from the effects of cold;" that young birds, kittens, human infants, &c., will survive a greater reduction of the actual temperature of their bodies than older animals. This may be a necessary adaptation of nature to the state of helplessness in which young animals exist.

It was probably, however, neither the youngest nor the older soldiers who survived the hardships of the retreat of the French army in 1812, but men in the greatest vigor of the prime of life. It would be an interesting question how far the mental foresight, the experienced endurance of the older veteran, may have compensated for the absence of the greater physical activity of youth. We may probably add to this the proposition that comparatively older animals suffer less from excess of heat. Elderly persons who visit warm climates are undoubtedly less liable to their peculiar diseases, than persons younger and in full health. It has been remarked that the recruits for the British army were far more effective when not chosen from among very young men.

Dr. Edwards says "There is scarcely any agent which exerts a more powerful influence on life than the temperature of the atmosphere, hence its relations are amongst those which it is the most important to know. There is, moreover, no agent which we have more in our power to modify and adapt to our necessities." We, undoubtedly, within certain limits, have the power of adapting temperature to our necessities; but on the grand landscape of the planet we do not control temperature. It is the sun's light that controls this agent. Temperature controls us.

In

spite of all our contrivances of shelter and of clothing, in spite of the arts of civilization, in spite of science, all the science we yet have on this subject, temperature controls us.

Great Britain, with her coal mines, has yet fuel enough for several centuries; and Pennsylvania, with her inexhaustible coal mines, can do much to modify the rigors of winter and to sustain a high civilization. But both these countries are among those most highly favored with a genial temperature; they are the very middle ground of average climate, where man is capable of his most fortunate development. If their coal was either at the equator or the poles, would it not remain unused forever?

As stated in a preceding chapter, the average temperature of the year at the Equator, 2777 miles south of Philadelphia, is equal to 88 degrees Fahrenheit, which is about the extreme heat of the hottest hours in the hottest days of midsummer, while at a similar distance north of us, which represents the more northern explorations, the average temperature of the year is Zero, which is about the extreme cold of the coldest hours in the coldest days of winter at Philadelphia.

The fathers of medical science, Hippocrates and Galen, among the ancients-Dr. Cullen and Dr. Hunter, of Britain -Dr. Rush, Dr. Wistar and Dr. Physick, of Philadelphiaand Dr. Liebig, of Geissen in Germany, the able writer on animal chemistry, have all been born and nurtured in the more fortunate intermediate climates.

Born and living in the temperate climates, these great men, although they have doubtless appreciated to a great extent the influence of climate, can scarcely be said to have extended their observations over the entire range of human existence. Their views were somewhat local, and their reflections on climate, therefore, and their reasonings