Argon was first isolated by Henry Cavendish in 1785, though he did not recognize it as a new element; it was not until 1894 that John William Strutt (Lord Rayleigh) and the Scottish chemist William Ramsay experimentally confirmed that argon was indeed a distinct element. Acting on a suggestion from Sir Madan, the President of the British Association for the Advancement of Science, they named the new gas "Argon" (derived from the Greek word meaning "inactive" or "lazy") and assigned it the chemical symbol Ar. The substance discovered at that time was, in reality, a mixture of argon and other inert gases; however, because argon constitutes the overwhelming majority of the inert gases present in the atmosphere, it was identified and characterized as the representative element of this group.
Separately, in 1882, H.F. Newall and W.N. Hartley, while observing the optical spectra of air in two independent experiments, detected spectral lines that could not be accounted for by any known elements; yet, they did not realize at the time that these lines signified the presence of argon. Ramsay subsequently removed all traces of nitrogen from the argon sample he had extracted from the air. Through spectroscopic analysis, he identified a new set of red and green spectral lines, thereby confirming the existence of a new element.
