Patented by Henri Herz in 1836, what was a dactylion designed to do?

The dactylion was specifically designed to loosen and strengthen the fingers of would-be virtuosos. It was made up of two parallel wooden bars. The first was fixed to the front of the keyboard and guided the hands. The second wooden bar, placed parallel to the first, had ten rings. These rings, one for each finger, were attached to springs that could be adjusted to give greater resistance.