from The Century Dictionary and Cyclopedia
- n. The space above the summit of the mercury column in any barometer. This space should be a (relatively) perfect vacuum: if it is not, then the correction or reduction to a vacuum should be determined by Arago's method.
Sorry, no etymologies found.
The jointed U-tubes of the vacuum-chamber are pressure-tempered colloid (no glass would endure the strain for an instant) and a junior engineer with tinted spectacles watches the Ray intently.