Sympiesometer by Heath & Co, London

This is a Sympiesometer by Heath & co limited,  Crayford, London S.E. Circa 1840. These instruments (this is an improved version) were briefly popular for a few decades up until around 1850 until the invention of the aneroid barometer, which proved to be more accurate and portable.  This led to the majority of the sympiesometer to be discarded ensuring the surviving instruments were to become rare.