pavement and houses are constructed of white stone. In the Arctic regions, the sun is, for six months in every year, above the horizon, and its light is reflected from the white snowy covering of the ground. The Esquimaux, who inhabit these inhospitable realms, suffer habitually from a weak state of the eyes; and those who have visited these parts complain much of the distress produced by the same cause. During the campaign of the French army in Egypt under Napoleon, a great number of the soldiers suffered from inflammatory affection of the eyes, which frequently resulted in blindness. This was attributed by Baron Larrey to the powerful light to which they were exposed, directly from the sun, and indirectly, by reflection, from the whitish, sandy soil. On a smaller scale, we observe similar results in individuals whose avocations expose them continually to very strong light,— as founders, blacksmiths, cooks, &c. Artificial light is far more fatiguing and irritating than that of the sun. Reading small type, and working at minute objects by lamp or candlelight, is apt, if habitually persevered in, to induce weakness of the sight, and after a time, more or less complete paralysis of the retina, and consequent partial or entire loss of vision. The great principle to be attended to, in artificial illumination, is to imitate, as much as possible, the diffused light of day; to have the lamp suspended above the head, and its light, if necessary, directed by a reflector upon our book or working. materials; care being taken that the source of the light does not too often strike upon the retina. A flickering, unsteady flame is par

ticularly to be avoided, from the irritation and annoyance it causes to the mind, and the fatigue to the eye, whose focus has to be re-adjusted with every movement of such flame. It is necessary that the light be sufficiently strong for a weak light fatigues the eye, by the sustained effort and attention necessary in order to work by it. It is desirable to avoid sitting too near to the source of light, on account of the heat given out in the process of combustion. Those who are compelled to work night after night by artificial light, as literary men, journalists, &c., and those whom poverty compels to ply the needle by the midnight rush-light, should, if possible, from time to time leave off their work, and allow the eyes to rest.

I should take but a narrow view of the subject did I consider the health of man as limited to the sound and vigorous condition of his body: did I exclude from my notice the influence which the presence or absence of light may exert upon his mind and spirit. Constituted as man is, light is indispensable to the development of his mental faculties. Without it, Nature's works would for him be

66 Expunged and razed,

And knowledge at one entrance quite shut out."

It reveals to him the forms and characters of objects in the organic and mineral worlds, tinting all things with characteristic hue,"clothing the garden and the meadow-glowing in the rubysparkling in the diamond," and giving rise to endless gorgeous effects of sky and atmosphere.

Justice has always been identified with light;

its character being to avoid secrecy and seclusion. The assemblies of the ancient British Bards, and after them of the Teutons, are said to have been held in "the eye of the light, and in the face of the sun," thus, at least, affecting justice, even if they exercised it not.

66

The state of man would indeed be hopeless, were his spiritual well-being to any degree dependent on mere physical agencies, and I do not, for one moment, mean to imply that such is the case. A certain cheerfulness, freshness and buoyancy of feeling, may be regarded as direct gifts of the sunshine," but sad would be his case, whose mind was not supported by higher and more spiritual illumination. Indirectly, however, physical light affects the moral health of humanity, inasmuch as darkness has ever been a cloak for iniquity. The darkest dens and hovels in all large cities and towns, have ever been the chosen resort of the vicious and criminal. It would be apart from the purpose of this work, to dwell longer upon this view of the subject. Job, speaking of futurity, says "there is no darkness, where the workers of iniquity may hide themselves," and our Saviour draws his illustration from the natural world, when He says "men loved darkness rather than light, because their deeds were evil."

Milton in his 'Paradise Lost,' associates with much effect his impersonation of moral darkness with physical.

"The fiend look'd up, and knew

His mounted scale aloft; nor more, but fled

Murmuring, and with him fled the shades of night."

CHAPTER III.

INFLUENCE OF HEAT ON PLANTS. ON ANIMALS.-WARM AND COLD-BLOODED ANIMALS.-INTERNAL HEAT OF ANIMALS AND MAN HOW PRODUCED.-CLIMATES AND ACCLIMATIZATION.-EFFECTS PRODUCED BY EXTREME HEAT OR COLD.-ARTIFICIAL HEAT.—

CLOTHING.-FUEL.

We

THE genial influence of heat, whether emanating from the orb of day, or from the humbler source of the domestic hearth, is felt by all. are all fully sensible to the exhilarating glow, the increased force of circulation, and greater activity of various functions induced by a moderate and healthful degree of this vital stimulus. But while admitting the facts, we may be ignorant of the cause, the reason of things. It is the part of the philosopher to endeavour to indicate these; to show the connexion between life and those natural conditions, on which Providence has thought fit to make it depend. In considering the vital influence of heat, the same course will be followed as when speaking of light. Its action upon plants and animals will first be considered, in order more clearly to elucidate the same upon the life and well-being of man.

The varying products of different parts of the earth, and the striking phenomena of the seasons, afford the most instructive and general illustration of the effects of heat. As we pass

from our own temperate country to the frigid regions of the north, we find vegetation becoming gradually scantier, and exhibiting itself in more spare and stunted forms; while the few animals that are destined to exist in these realms of ice and snow are furnished with special provisions to enable them to resist the destructive cold. If, on the other hand, we turn our steps towards the south, new and more highly-developed forms of animal and vegetable life everywhere meet our gaze, until in the tropical regions bordering on the equator, the luxuriance and beauty of nature is indeed marvellous. Nor need we seek a more satisfactory example of the action of heat in promoting life, than is presented in this and other temperate countries by the contrast between winter and summer. In winter the trees are despoiled of their foliage, the surviving verdure of the fields is perhaps concealed by snow, and the bosom of mother-earth locked up by frost. In summer, the renovating heat has again covered the ground with its verdant carpet, the trees and plants with leaves and variegated flowers and fruits; and the countless tribes of animated creatures are then rejoicing in the full vigour of being.

- Plants, unlike animals, possess no internal arrangement for the generation of the heat necessary to their well-being. The fluids absorbed by the delicate extremities of their roots at some distance below the surface of the soil, have a temperature, in winter somewhat higher, in summer rather lower than that of the atmosphere; and this temperature is retained when these fluids have ascended. along the sap-vessels of the plant.