WHEN electrified bodies are heated they are found to lose the power of retaining an electric charge. The charge leaks away from their surfaces. This is not a novel phenomenon. It has been known for nearly two centuries that solids glowing in air are capable of discharging an electroscope. Thus you observe that the electroscope is at once discharged when I bring near it a red-hot poker withdrawn from the furnace on the lecture table. These effects are due to the emission of ions by the hot solids. For example, if the electroscope is negatively charged it draws positive ions frorn the hot poker and so becomes discharged.