The surface of the stream soon cools and blackens, and the hard crust of nonconducting rock may grow thick and firm enough to form a tunnel, within which the fluid lava may flow far before it loses its heat to any marked degree.
"The Elements of Geology"
William Harmon Norton
The external radiation is regulated by the use of nonconducting plaster applied to the flue-plate and to the sides of the corner-flues, so that the heat is prevented from radiating in any direction except toward the oven.
"The American Woman's Home"
Catherine E. Beecher and Harriet Beecher Stowe