The word aneroid means not wet, or not a fluid, like mercury, so that, while aneroid barometers are being made which do use mercury, they are generally made without.
Such slight variations are more easily observed on the aneroid than on the mercurial barometer, and therefore it is commonly stated that the aneroid is the more sensitive instrument.
The mercury barometer is large and inconvenient to carry from place to place, and a more portable form has been devised, known as the aneroid barometer (Fig. 45).
There are two main types: manual, also called aneroid, and automatic.
Old scientific instruments such as aneroid barometers may provide some data but it will be patchy and data quality may be compromised though this can be checked by a suite of measurements on the other atmospheric gases.