Barometers Realm

The front of the case features a glass panel, allowing an unobstructed view of the intricate mechanism inside. The hinged top lid is secured with two hooks equipped with a special locking system to prevent accidental opening — a detail that reflects the meticulous attention to reliability required for aerial use.

Inside, a rectangular brass base supports the central mechanism of the barograph. A brass drum with a 4-hour rotation cycle driven by an hourly clock movement is the heart of the device, steadily rotating to record altitude changes over time instead of atmospheric variations.

The measuring element is an aneroid capsule, pressed by a triangular tension lever with an external coil spring at its apex. From this same point, a small connecting rod extends, which is hinged to the main rectangular lever. This main lever encircles a movable shaft, which is mounted in bearings with conical screws and rests on decorative brass legs.

The main lever is connected via a linkage to a short lever of the same shape, which is fixed to the recording shaft, also supported by brass columns. The short lever generates sufficient force to transfer rotational movement to the recording shaft. On the recording shaft, there is a large spiral spring, which prevents play in the levers. The recording arm is a long, flat spring, with the recording stylus mounted at its end. At the base of the stylus, there is a knurled brass adjustment screw, which allows fine control over the stylus pressure. To ensure that the stylus only touches the paper when the instrument is in operation, it is connected to a so-called locking lever—a long brass rod positioned next to the drum. Its free end protrudes outside the case in the form of a small lever, which can be adjusted without opening the instrument’s lid.

At the bottom of the case, there is a square shaft, into which a key is inserted to adjust the altitude setting, ensuring the proper positioning of the recording arm.

A brass arm extending from the mechanism ends with a fine writing pen, designed to trace atmospheric pressure fluctuations onto a paper chart. The chart is securely held in place by a flat brass plate, ensuring it remains steady during flight. On the outer front of the device, a small brass lever provides the user with the ability to disengage the writing arm from the drum — a practical feature for safeguarding the chart or resetting the mechanism.

On the cover of the recording altimeter, there are four upper attachment loops in the shape of hooks (the so-called tension loops), which were used to secure the instrument between the struts of a biplane’s wings.

Self-recording altimeters (also known as recording altimeters) are a special type of altimeter. They resemble barographs in appearance but operate on a different principle. Interestingly, the instrument’s cover is labeled as a barograph, which is likely due to the lack of a widely recognized short term for a self-recording altimeter in most languages—terms such as “Altigraph” or “Altimétrographe” never became standard. However, for example, the well-known company Short & Mason used the term “Altigraphs” in their instrument catalogs to refer to altitude recorders.

Self-recording altimeters have inverted and highly compressed scales. In barographs, higher pressure is positioned at the top of the scale, whereas in recording altimeters, lower pressure (corresponding to greater altitude) is placed at the top. Unfortunately, I was unable to obtain the proper altimetric charts for my instrument, so its drum currently holds a standard barometric chart.

The measurement range of this particular instrument, as indicated on its cover, is 5000 meters, where atmospheric pressure is approximately 400 mmHg (about 16 inches of mercury)—which is half of the sea-level pressure. As altitude increases, the scale intervals become smaller, since pressure decreases non-linearly.

Recording altimeters were used in both military and civilian aircraft to track altitude throughout flights. They allowed for flight trajectory analysis and aerodynamic adjustments. These instruments were employed in early research on the effects of altitude on engine performance and aircraft behavior. They were also installed on test aircraft to verify the accuracy of standard altimeters. In military applications, recording altimeters helped monitor the altitude of reconnaissance planes and bombers. Additionally, such instruments were mounted on balloons, airships, and stratospheric platforms for long-term altitude monitoring. They were used in high-altitude flight experiments, particularly for studying the upper layers of the atmosphere, where they recorded ascent and descent dynamics, aiding in the development of aerostat control systems.