Page:Notes on the State of Virginia (1802).djvu/226

212 walls. 3. So alſo on pavements of brick or ſtone. 4. It is more copious in proportion as the walls are thicker; the reverſe of which ought to be the caſe, if this hypotheſis were juſt. If cold water be poured into a veſſel of ſtone, or glaſs, a dew forms inſtantly on the outſide: but if it be poured into a veſſel of wood, there is no ſuch appearance. It is not ſuppoſed, in the firſt caſe, that the water has exuded through the glaſs, but that it is precipitated from the circumambient air; as the humid particles of vapor, paſſing from the boiler of an alembic through its refrigerant, are precipitated from the air, in which they were ſuſpended, on the internal ſurface of the refringerant. Walls of brick or ſtone act as the refrigerant in this inſtance. They are ſufficiently cold to condenſe and precipitate the moiſture ſuſpended in the air of the room, when it is heavily charged therewith. But walls of wood are not ſo. The queſtion then is, whether air in which this moiſture is left floating, or that which is deprived of it, be moſt wholeſome? In both caſes the remedy is eaſy. A little fire kindled in the room, whenever the air is damp, prevents the precipitation on the walls: and this practice, found healthy in the warmeſt as well as coldeſt ſeaſons, is as neceſſary in a wooden as in a ſtone or a brick houſe. I do not mean to ſay, that the rain never penetrates through walls of brick. On the contrary I have ſeen inſtances of it. But with us it is only through the northern and eaſtern walls of the houſe, after a north-eaſterly ſtorm. The r ſ e being the only ones which continue long enough to force through the walls. This however happens too rarely to give a juſt character of unwholeſomeneſs to ſuch houſes. In