This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
(German, Trdgheitsmittelpunkt; French Centre de giration.)
The centre of gyration "is that point at which, if the whole mass of a body rotating around an axis or point of suspension were collected, a given force applied would produce the same angular velocity as it would if ap-plied at the same point to the body itself." The distance of this centre of gyration from the axis of rotation is called the radius of gyration (German, Trdglieitshalbmesser; French, Rayon de giration); this latter is used in the calculation of strains, and is found by dividing the moment of inertia of the body by the area or mass of the body, and extracting the square root of the quotient, or, Square of Radius of Cyration.
(See Table I.)
A table will be given, later on, of the "squares of the radius of gyration" (German, Quadrat des Tragheitshalbmessers; French, Carre du rayon de giralion).