"The crystalline arrangement of atoms has an influence upon conduction of heat. Heat is conducted more rapidly in a direction parallel with the axis of crystallization than across that axis. Wood conducts heat more rapidly in the direction of the grain. This arrangement seems to be well adapted for keeping trees warm in winter. Their roots reach down into the earth, which remains warm in the coldest weather. This heat of the earth travels along the fibres up through the tree, while the heat conducted across the fibres escapes much more slowly into the open air. The bark also, being a very bad conductor, hinders the escape of heat. Of metals, silver is the best conductor. I will give you a brief table which will show the great difference in the conducting qualities of some of the metals. Counting the conducting qualities of silver as 100, the table is: 'Silver, 100; Gold, 53; Copper, 74; Iron, 12; Platinum, 8; German Silver, 6; Bismuth, 2.'--_Youmans._ "What is the second method by which heat passes from place to place?" "It is radiated," replied Ansel. "And what is radiation?" "It is motion in straight lines or rays diverging from a centre. From a hot body heat is passing off in straight lines in every direction. As a lamp radiates light, so does a hot body radiate heat." "Radiant heat," said Mr. Wilton, "moves with the same velocity as light, that is, one hundred and ninety-two thousand miles per second. It also follows the same general principles as light in all its motions. It is absorbed, reflected, or transmitted in the same manner as light. And this is true of either luminous heat--that is, heat radiated from a body which is red hot--or obscure, or dark heat. "As there are good and poor conductors, so there are good and bad radiators of heat. The radiation of heat depends upon three conditions: "1. Upon the temperature of the body. The higher the temperature, the more rapid and energetic is its radiation. "2. Upon the surface of the radiating body. A dull, rough surface radiates heat more rapidly than a surface bright and polished. "3. Upon the substance of the radiating surface. With surfaces equally smooth and bright, some substances radiate heat much better than others. A surface of varnish radiates heat much more powerfully than a surface of gold or silver. "Ansel, you may, if you can, explain the radiation of heat." "I can give no other explanation than that radiation is conduction through that subtle ether which is supposed to pervade all space."