invariable line

invariable line

[in′ver·ē·ə·bəl ′līn]
(mechanics)
A line which is parallel to the angular momentum vector of a body executing Poinsot motion, and which passes through the fixed point in the body about which there is no torque.
References in classic literature ?
It resulted from this invariable line of conduct that, as Conde and Turenne had never been conquerors of each other but under the standard of the king, Raoul, however young, had ten victories inscribed on his list of services, and not one defeat from which his bravery or conscience had to suffer.