Barometers Realm

Before us is a rare and technically outstanding Watkin Patent Aneroid Barometer, dating to approximately 1880, produced by one of the leading London instrument makers of the second half of the 19th century — James J. Hicks. The instrument belongs to the category of specialized scientific barometers with an extended scale and a multi-turn indicating system, intended for precise measurements in field and altitude conditions.

The barometer is housed in a compact cylindrical brass case. The construction is robust and of clear utilitarian design. At the top of the case is a substantial suspension ring mounted on a hinged support, allowing the instrument to be conveniently hung — both in fixed positions and during transport in expeditions.

The front is fitted with a thin rotating knurled bezel — a feature more commonly associated with pocket barometers. The bezel retains a flat mineral glass with a neatly faceted edge. This solution not only facilitates access for adjusting the indicator but also adds visual depth to the dial while providing protection against mechanical damage. Internally, the bezel is fitted with a reflective ring of silvered brass, improving the legibility of the readings.

Particular attention should be given to the unusual dial, executed in silvered brass. The barometric scale is graduated in London inches of mercury (inHg), ranging from 26 to 31 inches, and is arranged in the form of three concentric rings. Each ring covers an interval of two inches, together creating an exceptionally detailed scale divided down to one-thousandth of an inch — a remarkable degree of precision for aneroid instruments of its time.

Along the outer edge of each ring is an additional altitude scale in feet, extending up to 6000 feet, effectively turning the instrument into a combined barometer-altimeter. For correct reading of the indications, an ingenious solution is employed: at the lower part of the dial there is a small aperture displaying one of three Roman numerals — I, II, or III. These indicate which of the concentric rings should be read at any given moment, starting from the outer ring.

Another notable feature is the method of indicating pressure change. Instead of a traditional subsidiary pointer, a long, fine wire extends from the inner edge of the bezel toward the center of the dial. When the bezel is rotated, this wire moves freely across the dial surface, allowing the previous pressure reading to be marked simultaneously across all three rings — a solution that logically follows from the multi-ring dial construction.

The internal mechanism of the instrument is of no less interest. At its core is a German silver aneroid capsule, tensioned by a C-shaped steel spring, mounted on a substantial cast-iron lever, which in turn rests on two brass supports, ensuring stability and precise transmission of movement.

As indicated directly on the dial, the operation of the instrument is based on Watkin’s Patent multi-turn pointer mechanism. This replaces the conventional flat hairspring (which tends to buckle when the pointer makes multiple revolutions) with a fine cylindrical coil wound around the spindle, and introduces a helical groove (screw-thread “helix wheel”) on the pointer arbor, onto which a long fusee chain is wound, transmitting motion to the pointer shaft. Thus, the spindle itself acts as a winding drum for the spring, allowing it to operate over multiple turns without distortion. The helical groove interacts with the spring during operation, ensuring a smooth and controlled force.

A further refinement of the Watkin patent mechanism is the introduction of an auxiliary spindle with a secondary fusee arrangement, preventing spring deformation in extended-scale instruments. Unlike the fusee chain driving the pointer shaft, this system employs a very short length of fusee chain wound onto the axis of the main spindle, connected to the primary lever, which is temperature-compensated. This two-stage transmission allows the spring spindle to make more revolutions than the pointer, thereby reducing stress on the spring.

Thus, the advantages of Watkin’s 1886 Patent (UK No. 14,730), describing an improved aneroid barometer, lie in its extended range and reduced spring distortion, albeit at the cost of increased mechanical complexity and higher manufacturing precision. Few instruments incorporating Watkin’s design have survived, and his inventions saw limited adoption due to their cost and mechanical challenges.

The patent also describes an improved indication system for multi-ring dials: a movable index (a plate with multiple indicators — I, II, and III) mounted on a small extension of the fusee chain leading to the pointer arbor, indicating which concentric scale should be read. This allows successive revolutions of the pointer to be distinguished across overlapping scales without ambiguity.

This Watkin Patent barometer represents a rare combination of engineering ingenuity and craftsmanship. Its multi-ring dial, complex indicating system, and thoughtfully constructed mechanism make it not merely a measuring instrument, but an important milestone in the development of aneroid technology in the late 19th century. Such examples occupy a special place in collections, reflecting the period’s pursuit of increased precision and functionality in scientific instruments.