"The viola d'amore in love, Gall. Viola d'Amour, has six strings in all ... Its sound is otherwise argent or silver, therefore exceedingly pleasant and sweet. There are two types, large and small: The former are partly of a larger structure than the brazzers or violas, but the smaller ones are like the violins, except that the corpus is noticeably more perfect than the latter. ...
Nota. But there are six other brass or steel strings on this instrument, which reach out from under the hollow fingerboard, and at the bottom of the ordinary bridge into the iron strings attached above, superior to the upper chord, which can be tuned, but not bowed; therefore, they serve for nothing more than resonance."
[from: Joseph Friedrich Bernhard Caspar Majer, Museum Musicum Theoretico Practicum, Schwäbisch Hall 1732 (Facs.-Ed., Kassel, Basel 1954): § 13., p. 83.]