from The Century Dictionary.
- noun An apparatus for observing, measuring, or recording the intensity of high heats: a form of pyrometer for high heats.
- noun Specifically An apparatus of the kind which uses the tension of a vapor as a means of observing the heat, as that of the vapor of ether for lower ranges, and that of the vapor of mercury for greater. The vapor-tension moves a gage-needle over a dial, or a recording-lever may be moved across a moving disk or band of paper.
Sorry, no etymologies found.
Yet another principle is involved in the instrument called the thalpotasimeter, which may be used either with ether, water, or mercury.