The Convection and Conduction of Heat in Gases

Kennelly's data on The Convection of Heat from Small Copper Wires afford strong proof of the reliability and usefulness of the author's theory of convection. According to this theory, ``convection'' consists essentially in conduction of heat through a film of gas of definite thickness, in which the heat carried by motion of the gas is negligible compared to that carried by conduction, and outside of which the temperature is maintained uniform because of convection currents. The thickness of the film of gas is related in a simple way to the diameter of the wire, so that from the experiments the thickness B, which the film would have in. case of a plane surface, can be readily calculated. Previous results of the author have shown that 1. The quantity B, for quiet air at room temperature and one atmosphere prespure, is equal to 0.43 cm. 2. B is independent of the temperature of the wire, from room temperature up to the melting point of platinum, 1750 deg. cent. 3. The values of B obtained from experiments on wires of different sizes are found to be the same. In the present paper it is shown that Kennlelly's results confirm the above conclusions and furthermore lead to the following new conclusions: 4. The film thickness (for plane surface) B varies inversely as the 0.75th power of the pressure of the gas. 5. The value of B varies inversely as the 0.75th power of the wind velocity. 6.