A rare example of Sibson's instrument which was used as a combination of both percussion hammer and pleximeter. The weighted hammer was position centrally within a brass frame and could be raised by means of silk cords attached on either side. When dropped it would fall onto the ivory pleximeter from a fixed height and this would presumably have added a degree of consistency to the percussion note. The article is an extract from "PHYSICAL EXAMINATION OF THE CHEST, PULMONARY CONSUMPTION AND ITS INTERCURRENT DISEASES" by Somerville Scott Alison MD Edin. Published by John Churchill New Burlington Street in 1861