The microbarograph, or simply called a barograph, records atmospheric pressure in millibars adjusted to sea level.
A continuous record of pressure changes is recorded on a rotating cylinder wrapped precisely with graph paper.
The microbarograph is calibrated by the National Weather Service annually, and these barographs come in different shapes and sizes (3-day, 5-day and 7-day like the one we use at Pierce College).
The photo below shows how the pen arm travels across the rotating graph. The cylinder makes 1 full revolution every 7 days.
The barograph works by having the pen arm attached through a series of gears and levers to an aneroid cell. The word aneroid comes from the Greek roots a-, meaning without, and neros, meaning wet (loosely translated to English it means, “without fluid” or “fluidless”). The name holds true since aneroid barometers use no fluids in their function; rather they use aneroid cells composed of an alloy of beryllium and copper. There may be one or more of these cells, or capsules in any given aneroid barometer. This alloy is extremely sensitive to small changes in atmospheric pressure and expands or contracts as air pressure causing the pen arm to go down or up respectively on the graph paper. Upward motion of the pen arm indicates rising air pressure, downward motion of the pen arm indicates falling air pressure. The main difference between an aneroid dial barometer and the microbarograph is that the latter uses a pen arm mechanically linked to the aneroid cell(s) to move a pen arm continuously across a calibrated chart turning on a gear moved at a rate of 1 revolution every 7 days (or if it is a 3 day chart, every 3 days). Their functions, however, are the same. Though the mercurial barometer was invented by Torricelli, the aneroid barometer was the 1843 creation of Lucien Vidie, a French scientist. Aneroid was the perfect name for this new fluidless barometer as all others invented at that time thus far used fluids like mercury and water. Vidie’s invention was the first fluidless barometer (aneroid).
~ Steve Woodruff and Devin Lussier