INSTRUMENTAL a.
ablative. In Old English it was a separate case, but has disappeared, leaving only a few anomalous forms. Instrumental errors, those errors in instrumental measurements, etc., which arise, exclusively from want of mathematical accuracy in an instrument.
INTERFERENCE n.
, or, generally, two waves or vibrations of any kind, producing certain characteristic phenomena, as colored fringes, dark bands, or darkness, in the case of light, silence or increased intensity in sounds; neutralization or superposition of waves generally.