Conventional FT-IR instruments invariably use a voice coil drive to scan one or both mirrors of a Michelson interferometer, or one of the many variations on Michelson’s design. The scanning produces a profoundly accurate modulation of the incident radiation. The modulation can be decoded by Fourier transformation to recover a spectrum of the incident radiation. The reason that the mirror velocities are sharply limited is a result of the combination of mirror mass and the maximum linear motor force.