One historian states that in the 18th century,“it was becoming fashionable among upper-class households to own one of these useful instruments.” Wilton's barometer is an English (London) cistern type barometer by W & T Gilbert and Company with silver plate under a glazed window, ivory knob underglaze-which adjusts the vernier scale-- and swan’s neck pediment with brass mounts. The barometer also has a thermometer mounted on the front of the mahogany veneered case.
Barometers, invented by Evangelista Torricelli in 1643, are instruments used to measure atmospheric pressure. The word barometer comes from the Greek words meaning weight and measure. A glass tube from which the air was removed is put in a dish of mercury. Mercury is used in barometers because, “its weight made it possible to use a reasonably short tube.” As the air pressure increases it pushes down the mercury forcing it up the glass tube and when air pressure decreases the mercury is lowered back into the base. Air pressure is measured in “inches of mercury”or millibars (mb).
Air pressure is the force exerted by tiny particles of air. In the 17th century it was observed that there was a connection between the changes in the weight of air and those of the weather. As one source adequately puts it, “If a high pressure system is on its way,often you can expect cooler temperatures and clear skies. If a low pressure system is coming, then look for warmer weather, storms and rain.” Wind blows between areas of high and low pressure. Mr. Randolph might have owned a barometer as it would have proved useful for him and his livelihood of growing and selling tobacco from the plantation, which was contingent on the activity of the weather.
Many early barometers were made to fit the individual taste of those buying them. In the latter part of the 17th century and into the early 18th century barometers were constructed and sold by cabinet-makers, clock-makers, instrument-makers, and opticians. However, one historian attests that “as the nineteenth century wore on the quality of domestic barometers declined; and the death of inventiveness led to stereotyped designs in which only superficial variations were made.” Therefore, the year of this barometer can be placed by its design. Some characteristic designs in use in 1810, which are included in this cistern-tube barometer, are the mahogany frame, scroll pediment, and embellishments such as the use of ivory and wooden inlays. Also, a thermometer on the front of the case was a feature of the cistern-tube barometers of 1810. Leading makers around this time made their barometers in larger quantities and sold them to whole-sale retailers. It is their names that appeared on these later barometers.
In 1735, Edward Saul wrote in An Historical and Philosophical Account of the Barometer or Weather-Glass that barometers were in regular use in “most houses of figure and distinction.” It was no different later in the century when the Randolphs lived at Wilton, where the weather and temperature had a sway over the operation of the plantation and its cash crop, tobacco. It would not come as a surprise to see a barometer having a prominent place in an area of the house where Mr. Randolph would take care of the business of running his plantation. This provided him with a way of keeping an eye on what kind of weather to expect based on the rise and fall of the mercury.
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