Hi Joshua,

Thank you for contacting Mearto with your appraisal inquiry.
There are restrictions on selling mercury, which is why many auction houses decline to sell them but your barometer is quite similar to one that sold for $180 in 2021 (https://www.liveauctioneers.com/item/111259837_antique-mason-and-sullivan-admiral-fitzroy-s-barometer)
Based on the photos and information provided, and subject to examination, this is:

An antique Regency Masons & Sullivan's "Admiral Fitzroy's" barometer
English, late 19th Century
The rectangular mahogany frame with glass door and printed interior housing various scientific gauges and vials, including thermometer and barometer.
approximately 36 inches tall by 8-10 inches wide
CONDITION: appears to be in generally good condition; vials do not appear to be broken. Value assumes all elements are present and intact
PROVENANCE: acquired in a private sale
$150-200*
*represents a fair-market value for auction purposes; retail or asking price may vary.

Please let us know if you have additional items to appraise, and thank you again for using Mearto.