Baroˊmeter
Baroˊmeter [
an Instrument for estimating the Weight or Pillar of the Atmosphere, and the several
minute Variations of the Weight of that Pillar; by which Variations the various Changes
of the Weather are determined.
The first Inventor of it was Torricelli at Florence, in 1643. from whence Father Mersenne brought it into France the Year following 1644. and Monsieur Pascal tried it in 1646. and gave an Account of it in a Piece printed in 1647; the Uses
of this Instrument are to discover the Gravitation of the incumbent Atmosphere (one
of the noblest philosophical Discoveries) the Changes of the Weather, &c.
The Mechanism of the Barometer is as follows: A Glass Tube A B, hermetically seal’d
in A, having its Diameter about 1⁄10 of an Inch, and its Length at least thirteen Inches, is filled with Mercury so justly
as not to have any Air over it, nor any Bubbles adhering to the Sides of the Tube,
which is best done by means of a Glass Funnel, with a Capillary Tube; the Orifice
of the Tube, filled after this manner, so as to overflow, is closely pressed by the
Finger, so as to exclude any Air betwixt it and the Mercury, and thus immerged in
a wooden Vessel of a convenient Diameter, so, however as not to touch the bottom:
at the distance of 28 Inches from the Surface of the Mercury, are fix’d two Plates,
c e, and d f, divided into Inches, and these again subdivided into any Number of smaller Parts:
Lastly, the Tube is inclosed in a wooden Frame, to prevent its being broke, and the
Bason open, though secured from Dust.
Many Attempts have been made to render the Changes in the Barometer more sensible,
and so to measure the Atmosphere more accurately; which has given rise to a great
Number of Barometers of different Structures.
Hence comes the Wheel Barometer, Diagonal Barometer, Horizontal Barometer, Pendant
Barometer, &c.
A Marine Barometer being only a double Thermometer for Conveniency at Sea. See Thermometer.
Observations for the Use of the Barometer The Motion of the Mercury in the Tube does not exceed 3 inches in its rising and falling. The rising of the Mercury generally presages fair Weather, and its falling foul; as
Rain, high Winds and Storms. The falling of the Mercury in very hot Weather presages Thunder. The rising of the Mercury in Winter, foreshews Frost, and if the Mercury falls 3 or
4 Divisions in frosty Weather, a Thaw will certainly follow; but if the Mercury rises
in a continued Frost, Snow will follow. If soon after the falling of the Mercury foul Weather ensues, there will be but little
of it; and on the contrary, if the Weather proves fair soon after the Mercury has
risen, the same will happen. If the Mercury rise much and high in foul Weather, and continues so for 2 or 3 Days
before the foul Weather is over, then continued fair Weather will ensue. If the Mercury falls much and low in fair Weather, and continues so for 2 or 3 Days
before the Rain comes, then you may expect a great deal of wet, and very probably
high Winds. If the Mercury be unsettled in its Motion, it denotes uncertain and changeable Weather. As to the Words that are graved near the Divisions of the Instrument, though for the
most part the Alterations of the Weather will agree with them, yet they are not so
strictly to be minded, as in the rising and falling of the Mercury according to the
foregoing Observations; for if the Mercury stands at much Rain, and then rises up
to Changeable, it then foreshews fair Weather, although not to continue so long, as
it would have done if the Mercury were higher; so Places which are more Northerly
have a greater Alteration of the Rise and Fall of the Mercury, than those that are
more Southerly.
Definition taken from The Universal Etymological English Dictionary, edited by Nathan Bailey (1736)
Baptism [in Sea Language] * Wheel Barometer