The Collaborative International Dictionary of English v.0.48:
Sympiesometer \Sym`pi*e*som"e*ter\, n. [Gr. ? compression (fr. ?
to press together; sy`n with + ? to press, squeeze) +
A sensitive kind of barometer, in which the pressure of the
atmosphere, acting upon a liquid, as oil, in the lower
portion of the instrument, compresses an elastic gas in the
Note: The column of oil of a lower part BC of a glass tube
compresses hydrogen gas in the upper part AB, and is
thus measured on the scale pq by the position of a
surface of the oil in the tube. The scale pq is
adjustable, and its index must be set to the division
on the scale rs corresponding to the temperature
indicated by the termometer t, in order to correct for
the effects of temperature on the gas. It is sensitive,
and convenient for use at sea, but inferior in accuracy
to the mercurial barometer.