\He"li*um\, n. [NL., fr. Gr. ? the sun.] (Chem.)
A gaseous element found in the atmospheres of the sun and
earth and in some rare minerals.

\He"li*um\ (h[=e]"l[i^]*[u^]m), n. [NL., fr. Gr. "h`lios
the sun.] (Chem.)
An inert, monoatomic, gaseous element occurring in the
atmosphere of the sun and stars, and in small quantities in
the earth's atmosphere, in several minerals and in certain
mineral waters. Symbol, He; at. wt., 4. Helium was first
detected spectroscopically in the sun by Lockyer in 1868; it
was first prepared by Ramsay in 1895. Helium has a density of
1.98 compared with hydrogen, and is more difficult to liquefy
than the latter. Chemically, it belongs to the argon group
and cannot be made to form compounds. It is a decomposition
product of the radium emanation.