Thĕr/mo-tĕn'/sion, n.

n. [From Gr. θέρμη, heat, θερμός, hot, and Eng. tension.] A stretching by heat.

☞ This word has been applied to a process of increasing the direct cohesion of wrought iron. It consists in heating the metal to a determinate temperature, generally from 500 to 600 degrees Fahrenheit, and in that state giving to it, by appropriate machinery, a mechanical strain or tension in the direction in which the strength is afterward to be exerted.