original c. 1920's american industrial bourdon type mechanical steam gauge fabricated by the bogardus company, chicago, il. the oversized nickel-plated bronze bezel gauge was built for the hanley-casey company, chicago, il. the numerical dial and fanciful indicator are original and intact. the clear glass face plate is free from damage. the bourdon pressure gauge uses the principle that a flattened tube tends to change to be straightened or larger circular cross-section when pressurized. although this change in cross-section may be hardly noticeable, and thus involving moderate stresses within the elastic range of easily workable materials, the strain of the material of the tube is magnified by forming the tube into a c shape or even a helix, such that the entire tube tends to straighten out or uncoil, elastically, as it is pressurized. eugene bourdon patented his gauge in france in 1849, and it was widely adopted because of its superior sensitivity, linearity, and accuracy; edward ashcroft purchased bourdon's american patent rights in 1852 and became a major manufacturer of gauges. measures 7 inches in diameter.