What does dasymeter mean?
A dasymeter is a specialized scientific instrument designed to measure the density of gases, most commonly air. Its classic form, devised by the Scottish physicist Sir John Leslie in the early nineteenth century, consists of a sealed glass bulb attached to one end of a balanced beam: when the bulb is weighed in air and then in a near-vacuum, the difference reveals the buoyant effect of the surrounding gas, and hence its density. The name derives from the Greek words dasys, meaning thick or dense, and metron, meaning measure. Although the term appears chiefly in older physics texts and histories of instrumentation, it remains a precise and evocative word for anyone writing about classical experimental science. Today, similar measurements are usually performed with modern densimeters or electronic sensors, but the dasymeter stands as an elegant example of how simple mechanical principles can make the invisible weight of the atmosphere measurable.
nounA dasymeter is a scientific instrument used to measure the density of air or other gases, typically by weighing a sealed bulb in the gas and comparing it with its weight in a vacuum.
- An instrument for measuring the density of gases, especially air, by comparing the apparent weight of a sealed bulb in the gas and in a vacuum.
"The physicist calibrated the dasymeter carefully before measuring the density of the gas in the chamber."
"Using a dasymeter, the students demonstrated that warm air is measurably less dense than cold air."
"The laboratory's antique dasymeter, built on Leslie's principle, still gave reliable readings after two centuries."
Standard English plural; the word follows regular noun inflection.
"Early laboratories often kept several dasymeters for comparing gases at different temperatures."
Invented by Sir John Leslie in the early 1800s, the dasymeter weighs air itself — turning something invisible into a number you can hold.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dasymeter
The word dasymeter comes from Greek roots: dasys, meaning 'thick' or 'dense', combined with -meter, from metron, meaning 'measure'. It was coined in the early nineteenth century for Sir John Leslie's instrument for measuring air density. The same Greek combining forms appear in related scientific vocabulary such as densimeter, barometer, and hydrometer.
How dasymeter is actually used
A rare, technical term confined to historical and scientific contexts; most modern gas-density measurement uses instruments described as densimeters or electronic sensors rather than dasymeters.
Easily confused with dasymeter
A densitometer measures optical density, such as the darkness of photographic film, whereas a dasymeter measures the physical density of gases.
A dosimeter measures exposure to radiation, while a dasymeter measures the density of gases.