This is a matter of no small importance, yet, how often do we see it treated not only with indifference, but upon the very worst principles possible to ensure its preservation; not one ice-house in fifty is constructed upon correct principles - not one in the same number is managed correctly.

When we consider that damp and heat are the two great agents for thawing, it should be our endeavor to counteract these by every means in our power. To effect this, ventilation must be had recourse to, and non-conducting materials employed in the erection. Of materials, we may observe, that stone is, of all others, the worst; timber and brick are the best. The usual practice of sinking ice-houses to a great depth under the surface is bad; indeed, it has only one redeeming property, which is the convenience of filling from the top. Its disadvantages are, the difficulty of admitting sufficient ventilation to correct the dampness, which, build them as we may, is sure to exist in underground houses; the conduction of heat from the surrounding soil, and the difficulty of effecting sufficient drainage: these very far overbalance the advantages thus offered. Why are the majority of ice-houses, and most cellars during winter, so much warmer than the surrounding atmosphere? Is it not from the heat conducted through their walls from the surrounding soil? Earth is a much better conductor of heat than air, or, in other words, it communicates its heat to other bodies coming in contact with it, much quicker than that element.

Hence the necessity of placing between the earth and the ice some slower conductor of heat, and the slowest conductors we have applicable to the case, are timber or air; both also, resist damp, while stone does not, and besides, it is a rapid conductor of beat. Water is also a rapid conductor of heat, and instances have been known where rain water has percolated through the roof of an ice-house, that the temperature within has been raised to 60°. Hence the necessity of keeping such houses perfectly dry, not only at top, but also all throughout, by efficient drainage of the melted ice. and by ventilation to correct the dampness in the atmosphere and walls. Indeed, the walls of an ice-house, to be in a proper condition, should be as dry as those of a dwelling. Ventilation, if properly applied, will, in most cases, effect this, and should it not, the introduction of a few bushels of unslacked lime, occasionally placing it in boxes over the ice, will completely dry the walls without elevating the temperature much, if the ventilators be open at the keeping; and so it would, if kept in a state of quiescence, but this is impossible, owing to the difference of temperature which will exist in that portion of the air coming in immediate contact with the surface of the ice, whether on the top or around the side of the mass, which will be reduced to a much lowor temperature, say nearly 82°, than that in contact with the walls of the house, if sunk under the surface, from its receiving heat by conduction through them, so that it is often found to be as high there as 46° or 47°; this difference of temperature causes circulation to take place, the lighter air ascending upwards, seeking for escape, and becomes replaced with the colder and more weighty.

It follows, therefore, that if this circulation could be interrupted, the melting action on the ice would be greatly diminished, and a state of quiescence secured. This appears, however, to be impossible. - North British