The London ClockMaker

A mercury barometer has a glass tube of at least 33 inches (about 84 cm) in height, closed at one end, with an open mercury-filled reservoir at the base. The weight of the mercury actually creates a vacuum in the top of the tube. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir.

High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir. Since higher temperature at the instrument will reduce the density of the mercury, the scale for reading the height of the mercury is adjusted to compensate for this effect.

A SELECTION OF THE BAROMETERS FOR SALE AT OUR SHOP:

Stock No: 042

Stock No: 043

Stock No: 046