The term has been used in natural philosophy and physics to explain certain mysterious phenomena as the result of fluids with properties which defy the imagination (or at least differ from the conventional properties of fluids). The term is used in contrast with ponderable matter. Historically proposed imponderable fluids include phlogiston and caloric; additionally some physicists considered electricity imponderable.
Leibniz mentions with great disapproval a certain Hartsoeker who supposed that atoms moved in an ambient fluid, though the idea is not unlike his own. It is difficult to trace the origin of the hypothesis, but Galileo and Hobbes both speak of a subtle ether. The conception of an all-pervading imponderable fluid of this kind has formed part of many theories, and ether came to be very generally adopted as a favourite name for the fluid, but caloric was also much thought of as a medium. We even find half-a-dozen imponderable co-existent fluids regarded with favour,—one called heat, another electricity, another phlogiston, another light, and what not, with little hard atoms swimming about, each endowed with forces of repulsion and attraction of all sorts, as was thought desirable. This idea of the constitution of matter was perhaps the worst of all. These imponderable fluids were mere names, and these forces were suppositions, representing no observed facts.
The electric fluid
Study of the laws which govern electrical forces, let an apparatus be provided, called an electric pendulum. Effects were explained by the supposition that a subtle and imponderable fluid developed upon the glass tube which is self-repulsive; that by touching the balls, a portion of this fluid has been imparted to them, which is diffused over their surface, and which, for reasons that will hereafter appear, cannot escape by the thread of suspension; that the fluid remaining on the glass tube repels this fluid diffused on the balls, and therefore repels the balls themselves which are invested by the fluid; and, in fine, that the fluid diffused on the one ball repels and is repelled by the fluid diffused on the other ball, and that the balls being covered by the fluid are reciprocally repelled. A vast body of phenomena had converted this supposition into a certainty for the time, accepted by all scientific authorities. The fluid producing these effects was called the "Electric Fluid", now called the electric field.
M. Martin Ziegler patented a method of producing a "vital fluid" by combining nitrogen and carbon in a porous cell containing ammonia, immersed in a vessel tilled with molasses. The current was to flow through silk threads attached to the vessel: about 1868.
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- Textbook of Human Physiology, Leonard Landois , William Stirling, 1889
- Scientific Realism: How Science Tracks Truth, Stathis Psillos, 1999, Routledge
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- U.S. patent 60986, Improved imponderable fluid, and mode of generating the same. Jan 1, 1867.
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