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Aug 17, 2009
Contributed by Ian Tresman
August 22, 2009 this week will mark the 130th anniversary of the identification of "radiant matter" or "plasma" as the fourth state of matter in 1879, by English scientist, Sir William Crookes, (1832-1919).
Sixty years earlier, Michael Faraday had postulated "radiant matter" as "purely hypothetical". On 17 January 1816, Faraday delivered a series of lectures to the City Philosophical Society, one of which was titled "Radiant Matter".
"If now we conceive a change as far beyond vaporisation as that is above fluidity, and then take into account also the proportional increased extent of alteration as the changes rise, we shall perhaps, if we can form any conception at all, not fall far short of radiant matter"
By 1819 Faraday considered:
"Matter classed into four states solid, liquid, gaseous, and radiant which depend upon differences in the essential properties. [..] I have purposely avoided mentioning the radiant state of matter, because, [it is] purely hypothetical.."
On Friday August 22, 1879, Crookes delivered a lecture titled "On Radiant Matter", to the British Association for the Advancement of Science in Sheffield, England.
"To throw light on the title of this lecture I must go back more than sixty years to 1816. Faraday, then a mere student and ardent experimentalist, was 24 years old, and at this early period of his career he delivered a series of lectures on the General Properties of Matter, and one of them bore the remarkable title, On Radiant Matter.
"[..] the experimental results are obtainable to which [are] so distinct are these phenomena from anything which occurs in air or gas at the ordinary tension, that we are led to assume that we are here brought face to face with Matter in a Fourth state or condition, a condition as far removed from the state of gas as a gas is from a liquid."
"[..] they assume properties so novel and so characteristic as to entirely justify the application of the term borrowed from Faraday, that of Radiant Matter."
Among other properties, Crookes discovers that:
"Radiant Matter is deflected by a Magnet" and "If the streams of Radiant Matter carry an electric current they will act like two parallel conducting wires and attract one another ; but if they are simply built up of negatively electrified molecules they will repel each other."
It was nearly 50 years later, in August 1928, that Irving Langmuir coined the term "plasma".
The life and letters of Faraday (1870)
Jones, Henry Bence, 1814-1873
http://www.archive.org/details/lifelett ... 01joneuoft
On radiant matter: a lecture delivered to the British Association for the Advancement of Science, at Sheffield, Friday, August 22, 1879.
Crookes, William, Sir, 1832-1919
http://www.archive.org/details/onradian ... 00croorich
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