16—7.
THE MCLEOD GAUGE
365
The volume
a is equal to 7r72h, where 7 is the radius in mm. of the
un1formly
c1rcular capillary bore (determined when the gauge Was
being manufactured) and & is the distance in mm. to the top of the
D
FromVacuum
,
System
(1)
@
V
V
…
(?.)
76
To
…
F
8
FIG. 16—9.
Pressure gauges.
capillary. In the other side tube, the mercury rises to D, so that
P = ]z’, in mm. of mercury.
This side tube is made of the same
capillary tubing as C in order that there shall be equal capillary
depression on both sides. We then have,
2
/
p :
mm. of mercury,
(16—4)
V being measured in cubic millimeters. The gauge may be
operated conveniently by making /z' = &. Then we have
})
=K/
(16—5)