On a peculiar source of deterioration of the magnetic powers of steel bars

The author concludes, from various experiments on the changes in the magnetic force of steel magnets produced by subjecting them to blows with a wooden mallet, or other modes of creating tremors or vibrations among their particles, that the most apparently trifling mechanical agitation is sufficient to occasion a considerable diminu­tion of magnetic power; that this loss, when it has taken place from such a cause, is permanent; and that in every case, after reaching a certain point, it attains its maximum, a fact which implies, in every magnet, the possession of a specific retentive force, of which it can­ not be deprived by any further mechanical commotion of its particles. The more highly a bar is magnetized, the more it becomes susceptible of a loss of power by agitation.