This is a sensitive precision instrument that was probably used as a standard for evaluating instruments sent to meteorological field stations. The mercury-in-glass thermometer is mounted on a white porcelain plate marked "NEGRETTI & ZAMBRA, SCIENTIFIC INSTRUMENT MAKERS, LONDON" and "ABSOLUTE" and "29" with the M/O monogram of the British Meteorological Office, the N/Z monogram of the firm, and the K/O monogram of the Kew Observatory.
The plate is graduated every 5 degrees from 245 to 325. The back of the stem is white enamel and marked "29" and with the M/O and N/Z monograms; the front is graduated every degree from +243 to +325 and numbered at 245, 273, and 320. It came to the Smithsonian from the U.S. Weather Bureau.
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