Double or “four-tube” barometers use a late 18th century design for an instrument more compact than the nearly 40-inch length of mercury-filled glass tubing of conventional barometers. The single column is replaced by two shorter tubes: the mercury fills two parallel tubes, alternating with oil in the other two.
The scale that displays movement is then five times the normal length, making small changes of atmospheric pressure much more readable. The backplate is a sheet of light-colored boxwood with the numbers and lines cut or pressed in and filled with black wax, and includes a red spirit thermometer. A mahogany-framed glazed door protects the scale. This instrument was signed Baptista Ronchetti Fecit.
Circa 1785-1810
22.75” high, 5.75” wide
sold
Charles Edwin Inc.
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