The first is a mercurial barometer, which measures atmospheric pressure by balancing a column of mercury against the weight of the air.
(The first; is; a mercurial barometer, which measures atmospheric pressure by balancing a column of mercury against the weight of the air) (a mercurial barometer; measures; atmospheric pressure; by balancing a column of mercury against the weight of the air)
The first a mercurial barometer
is measures
a mercurial barometer, which measures atmospheric pressure by balancing a column of mercury against the weight of the air
atmospheric pressure by balancing a column of mercury against the weight of the air