Ramsay’s curiosity was piqued by Lord Rayleigh’s observation that the density of nitrogen extracted from the air was always greater than nitrogen released from various chemical compounds. Ramsay then set about looking for an unknown gas in air of greater density, which—when he found it—he named argon. While investigating for the presence of argon in a uranium-bearing mineral, he instead discovered helium. This second discovery led him to suggest the existence of a new group of elements in the periodic table. He and his coworkers quickly isolated neon, krypton, and xenon from the earth’s atmosphere.