If you lay your hand upon the woollen table cover, or upon the sleeve of your coat or mantle, it will feel neither warm nor cold, under ordinary circumstances. But if you raise your hand from the table cover, or coat, and lay it on the marble mantel piece, the mantel-piece will feel cold. If now you return your hand from the mantel-piece to the table cover or coat, a sensation of warmth will become distinctly perceptible. This will afford a good conception of the relative powers of conduction of wool and marble.
139. How long does a substance feel cold or hot to the touch?
Until it has brought the part touching it to the same temperature as itself.
140. When do substances feel neither hot nor cold?
When they are of the same temperature as our bodies.
141. Why, under these circumstances, do they feel neither hot nor cold?
Because they neither take heat from, nor supply it to, the body.
142. Which would feel the warmer, when the fire was lighted, the hearth-rug or the hearth-stone?
The hearth-stone, because it is a good conductor, and would not only receive heat readily, but would part with it as freely (thereby making its heat perceptible). But the hearth-rug, being a bad conductor, would part with its heat very slowly, and it would therefore be less perceptible.