A pulse glass consists of a narrow tube bent at right angles at either end, with two larger spheres on the ends.
The pulse glass was brought to the attention of the scientific world by Benjamin Franklin in a 2 July 1768 letter to John Winthrop (, v.
The first and probably most important feature of the pulse glass is that it embodies a phenomenon so compellingly.
The quick evaporation occasioned in vacuo by a small degree of heat is agreeably seen in what is termed a pulse glass, [...] (Darwin , vol.
Even long after the pulse glass was recognized as a technologically certified striking phenomenon, its theoretical context remained unclear.
Benjamin Franklin's previously cited account of the pulse glass reveals that he appreciates the phenomenon under at least two descriptions: (1) bubbles 'were continually passing day and night', i.e.
Franklin's readiness to associate (3) with the rather implausible 'fact' reported by Aristotle testifies to the striking power of the pulse glass: it introduced cognitive dissonance, leading Franklin to question what otherwise would have remained unquestioned common knowledge.
If Franklin's interest in Aristotle's strange fact reveals the extent of his sheer puzzlement, James Watt provides a description of the pulse glass from an entirely different point of view.
The invention of the pulse glass is ascribed to Dr.
Why should Watt care whether the pulse glass was invented before or after his improvement on the steam engine?
Since Watt's views on the relationship between heat, work, pressure, and the elasticity of steam are now considered obsolete (Baird ), it would have to include contemporary theoretical jargon--(7)--that the pulse glass represents a reversible isothermal transformation.
All the while, the pulse glass remained technologically stable.