Argon

The atomic weight of nitrogen was found to vary based on its source. To resolve this inconsistency Ramsay used the same technique Cavendish used to discovering hydrogen. The result was a verifiably new gas, proven through spectrometry. He called this new element argon ("inert" in Greek).
 John William Strutt and William Ramsay Scotland 1894 Argon

The atomic weight of nitrogen was found to vary based on its source. To resolve this inconsistency Ramsay used the same technique Cavendish used to discovering hydrogen. The result was a verifiably new gas, proven through spectrometry. He called this new element argon ("inert" in Greek).