The operation of rotating machines at high altitudes and of motion- transmitting devices in reactors is made difficult by the high wear and friction of sliding surfaces in a dry atmosphere. The friction of different grades of carbon on metals and on carbon itself was studied in dry atmospheres of oxygen, nitrogen, and carbon dioxide and in a humid atmosphere. The chemically or physically active gases, oxygen, carbon dioxide, and water, affect the wear and friction more than nitrogen. Friction and wear of carbon is related to the properties of gas adsorption. (J.S.R.)