1958. Prepared coverings are double mats with a layer of hay or straw within, like mattresses; they are used for covering hotbeds in mid-winter, but are readily rendered injurious by heavy rains. A mode which would produce the same effect, is to use three thicknesses of mats, keeping them apart by small frames of lath or hollow rollers; the object being to preserve vacuities or strata of air between the glass and first mat, between the first and second mat, and between the second and third mat, which, if attended to, would resist any external cold whatever without cumbrous loads of hay, straw, &c. (See Dr. Wells on Dew, and Remarks on Hothouses, &c.)
