ŁM-1M barograph

Instruments for measuring pressure were known as early as the 17th century as a result of research by Evangelista Torricelli (1608-1647), an Italian mathematician and physicist, secretary to Galileo Galilei, who carried out the experiment underlying the design of the liquid barometer. However, it was not until the 1860s that the first operational device to record barometer readings was invented by Alexander Cumming (1733-1814), a Scottish watchmaker and inventor. Barographs constructed in line with his method of operation included barometers involving aneroids, and pressure sensors, the essential part of which is a vacuum membrane can, also known as a Vidi can. The deformation caused by changes in pressure inside it, for barometers, is transmitted to the pointer, and for barographs, through a lever mechanism fitted with a marker or pen at the end, the result of the pressure measurement is recorded on a barogram, a paper tape with a time scale. The barogram is placed on a rotating drum that moves clockwise. Depending on the design of the device, and in some models on the user's preference, the drum makes one revolution per day, week or month. Marine barographs used on ships have also often used the effect of vibration damping to offset recording interference caused by the constant motion of the ship on the waves. This was achieved by oil damping of the recording mechanism or by simple spring legs attached to the base of the device. A Soviet barograph manufactured in 1968 in Riga is provided with a barogram printed with a time scale on a 7-day cycle, where each day is divided into 12 two-hour units. The vertical pressure gradient, on the other hand, is scaled from 950 to 1050 hPa with horizontal auxiliary lines every 10 hPa. Leszek Kocela