An increase of the temperature of the air increases its elasticity and decreases its density. We might, therefore, expect sound to travel more rapidly in warm than in cold air. Experiment confirms the conclusion. There is an added velocity of about 1.12 feet for every Fahrenheit degree, or of about 2 feet for every centigrade degree of increase of temperature. (The freezing temperature is 32deg. F, or 0deg. C.)