Fronticepiece for Humphry Davy’s “Researches, Chemical and Philosophical”, published in 1800. A mercury-seal gasometer that predates Hutchinson’s spirometer by over 40 years. The counterweight is attached to a cam that varies the force over the range of motion of the bell. This device was used as an air holder, not as a measuring device since the only scale for volume was a uncalibrated dial on the cam. Found on PublicDomainReview.com.