The Collaborative International Dictionary of English v.0.48:

Stethometer \Ste*thom"e*ter\, n. [Gr. ? chest + -meter.]
   (Physiol.)
   An apparatus for measuring the external movements of a given
   point of the chest wall, during respiration; -- also called
   thoracometer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Thoracometer \Tho`ra*com"e*ter\, n. (Physiol.)
   Same as Stethometer.
   [1913 Webster]