Barometers Realm

Barometer’s body is crafted from brass and includes a hanging ring. The delicate rotating fluted bezel on the front is secured to the case with three tiny screws. The bezel incorporates a brass reflective ring and a thin band with an altimeter scale made of silvered brass. Finally, the bezel is topped with protective flat glass with beveled edges.

Barometer’s dial is made of silvered brass and has an unusual stepped design. The barometric scale, graduated to 1/50th of an inch and marked in London inches of mercury, is positioned on the raised portion. Notably, there are no weather-related text indicators on the scale.

The plateau of the dial bears the manufacturer’s name and notes that the barometer is compensated. It also includes a third scale — a Fahrenheit thermometer scale — positioned in a semicircle and accompanied by a mercury thermometer.

The barometer’s indicator hand is made of blued steel, featuring a crescent-shaped feather at its tip.

The corrugated shallow metal chamber can be seen towards the back of the frame plate and above it is a powerful curved spring resting in gudgeons fixed on the frame plate; the spring suspends the vacuum chamber. A lever, attached to the top edge of the spring, is connected to a second lever attached to the frame plate; a pin from this lever is connected to a chain, the other end of which is coiled round, and fastened to, the arbour. The indicating hand is fixed to the arbour. There is also a spiral spring attached to the arbour which keeps the chain taut.

The shape of the bridge and the plates surrounding the indicator shaft is characteristic of the well-known London instrument maker Casella. Therefore, it is likely that MacDonnell acted as Casella’s retailer in Sydney.