Cardan's Suspension

Device employed in suspending a barometer tube or other instrument which is required to maintain a vertical position. The case containing the tube turns about a horizontal axis fixed to a ring or thimble, which in turn is movable about a similar axis at right angles to the former one. By means of this double suspension the barometer is movable in all vertical planes, and as its center of ma is below its point of support, the position a umed will always be vertical.