Figure, 'Sphygmoscope' by S [Somerville] Scott Alison A figure of Alison's sphygmoscope, labelled figure 1: 'The sphygmoscope (fig. 1.) consists of a small chamber containing spirits of wine or other liquid, provided with a thin india-rubber wall, where it is to be applied to the chest. At the opposite extremity the chamber communicates with a glass tube, which rises to some height above the level of the chamber. Liquid is supplied to the instrument until it stands in the tube a little above the level of the chamber. The pressure of the column of liquid in the tube acts upon the elastic or‘yielding wall of india-rubber and causes it to protrude. This protruding part or chest-piece is very readily affected by external impulse; it yields to the slightest touch, and being pushed inwards, causes a displacement of the liquid in the non-elastic chamber, and forces a portion of liquid up the tube'. Subject: Scientific apparatus and instruments 1856