any other method would have had a chance of succeeding with such damp materials."

Dr. Arnott gives the following table, in which the relative value of different substances used as fuel is shown by their power of melting a relative quantity of ice :

One pound of good Coal melts of ice

90 lbs.

84

95

32

19

Now, wood charcoal is produced by submitting wood in a chamber from which air is excluded, to a very high temperature, by which certain component elements are driven off. This preliminary process diminishes its availability as fuel; consequently, in countries where it abounds, coal, from the heat it gives out in burning, is the cheapest and best fuel. It is satisfactory to think that in the mines of this country, there is sufficient store for more than a thousand years. Man in earlier ages used wood, and this is the fuel still had recourse to in countries where coal is scarce, and by the poor peasants in our own land. In some countries, the peasantry use peat; and in some of the barren districts of Brittany, visited by me in summer-time, I found the walls of the little stone houses of the poor inhabitants covered with circular or hexagonal patches of manure, placed there to dry for winter consumption. Among other hints given by Dr. Arnott in reference to fuel, and the modes of using it, there is one which seems well worth the consideration of the poor. "It is wasteful to wet fuel, because the moisture in being eva

porated, carries off with it as latent, and, therefore useless heat, a considerable proportion of what the combustion produces. It is a very common prejudice, that the wetting of coal, by making it last longer, is effecting a great saving; but it does so merely by restraining the combustion, or producing a smaller fire, and with the bad fire, there is also much waste of heat. To illustrate the influence of watery vapour upon combustion, we may mention the fact, that a manufacturer who tried to blow his fire, by forcing steam into the furnace with the air, extinguished his fire; and the analogous fact, that ordinary fires burn better in winter than in summer, although the temperature be lower, because cold air is generally much drier than that which is warm.

Although a moderate amount of clothing coupled with exercise is, ordinarily, sufficient to maintain the heat of the body in cold seasons and climates; when man is in a comparative state of repose, he is either obliged, as during sleep at night, to increase the amount of covering, or, in his usual in-doors life in the day-time, to warm artificially the air of the room in which he sits. This artificial warmth is produced either by radiation from the open fire, or a close stove, or by causing hot air or water to circulate in pipes or flues round the room. The latter mode of warming has the advantage of maintaining different parts of the room at a more even heat, of enabling us to regulate this better, and of not distracting our attention, as does an open fire, from any work in which we may be engaged. On the other hand, our English feelings, and in some

measure our social life are bound up with the fireside; and when we consider the cheering, moral influence of the blazing log or coal fire, we shall not be disposed to give up such old friends for doubtful new ones. And indeed, it is now pretty clearly proved that a modification of the open hearth, meets most effectually the twofold object of heat and ventilation. The subject will be considered further in another chapter. The temperature of the room should not be too high, or the contrast, when we are compelled to go out into the cold air, will be strikingly felt. A few degrees above temperate heat, about 60°, will suffice for ordinary purposes. Some persons who do not possess the power of generating internal heat in a very vigorous degree, are more dependent on artificial heat, and may require a temperature higher than that just indicated. It is necessary, in damp and cold weather, that there should occasionally be a fire in the sleeping apartment; although the habitual recourse to it tends to enervate. Persons of delicate constitutions, especially those suffering from pulmonary affections, asthma, consumption, &c., should have a fire lighted in the bed-room two or three hours before the time at which they retire to rest, so that on entering the apartment, they may breathe air as dry and warm as that they have left. Attention to this point is of essential importance in the treatment of such diseases. In all large dormitories, as those of schools, asylums, and workhouses, the frequent use of a fire for an hour or two in the day-time during cold and damp weather, will diminish in a remarkable degree the tendency to colds, coughs,

rheumatism, &c. The maintenance of an equable temperature, is part of the ordinary regime in the wards of our hospitals, and is of no less moment in the private treatment of disease. There is another point worthy of notice in reference to artificial warmth. "After an exposure to cold, sufficient to diminish the power of producing heat, continuance in a high temperature tends to the recovery of this power; for in exposing animals to successive applications of cold, their temperature will fall the more slowly, the longer they shall have been subjected to the influence of warmth. It follows, therefore, that the effect of the application of a certain degree of heat is continued after the cessation of the cause, furnishing the counterpart of what we have stated with respect to the application of cold. Hence, we see that those who are liable to frequent exposure to severe cold, are rendered more capable of supporting it, by subjecting themselves, in the intervals, to a high temperature; a practice adopted by northern nations, and justified by the foregoing facts."

I have thus shown the importance of preserving the human body from the prejudicial effects of extreme heat or cold, and the means to be pursued in order to accomplish this. I have also, in showing the arrangement by which the temperature of the body is maintained, at a pretty uniform standard under opposite conditions of climate, exhibited to the thoughtful and reflecting, another marvellous instance of Providential design.

Edwards on Influence of Physical Agents on Life.

CHAPTER IV.

AIR, ITS IMPORTANCE TO ANIMAL AND VEGETABLE LIFE.-PROVISIONS FOR RESPIRATION IN ANIMALS AND MAN. MECHANISM OF RESPIRATION IN MAN.-CHEMICAL CHANGES INDUCED BY IT. -CAUSES THAT INTERFERE WITH EFFECTIVE RESPIRATION IN THE INDIVIDUAL AND IN COMMUNITIES.-VENTILATION.EPIDEMICS.-ELECTRICAL AND HYGROMETRIC CONDITION OF AIR. CHANGE OF AIR.-SANITARIA AND SANATORIA.

THE atmosphere which envelops man and other organized beings on the earth's surface, may, on many grounds, be regarded as the most essential and indispensable of physical agents. In a direct sense, it is "the breath of life"-maintaining through respiration the nourishment and vital warmth of the body; while indirectly, it contributes to our well-being, as the medium through which other physical agents, light, heat, electricity, and watery vapour, are enabled to exert their influence. But, although the gales of Heaven ordinarily bear to us renovation and health, they are too often, through our own folly, charged with the elements of disease; and at times, are made the vehicle of God's scourges, of "the pestilence that walketh in darkness," or, "the destruction that wasteth at noonday."

I shall, in the first place, consider the atmosphere in its healthful action upon organized beings, and subsequently, notice the various causes by which its sanitary influence may be impaired.