Wheel Barometer (c. 1720) by George Graham

In the museum of Colonial Williamsburg, VA.

The text of the museum's description (from the next photograph):

"This magnificent barometer, one of only several wheel barometers surviving from the early eighteenth century, is one of two barometers known to have been made by George Graham (1673--1751). Graham was apprenticed to Thomas Tompion, married his niece, worked as his partner, and assumed the business upon his death. Graham's fame, however, rests upon his own achievements in the field of horology and instrument making, and he is credited with a number of major horological inventions and known for the superb quality of his products.

"Not surprisingly, the design of the upper portion of the case of this barometer resembles that of contemporary bracket clock cases. Inside the case is a glass tube containing mercury. The barometric pressure determines the height of the mercury in the tube, and a float resting on the mercury controls the long steel hand of the dial by means of a cord and pulley arrangement. The larger brass hand is adjusted manually by the knob above the signature to indicate rising or falling pressure, and the two flanking knobs are adjusted manually to indicate the date."

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