Argon

Argon (Argon, Ar; Greek средн. a sort from argos – inert, inactive) – chemical element VIII of group of periodic system of elements of D. I. Mendeleyev, atomic mass (weight) – 39,948; atomic number – 18; inert gas, is applied to preparation of respiratory narcotic mixes in anesthesiology.

 
Whether you know that:

In operating time our brain spends the amount of energy equal to the 10 Watts bulb. So the image of a bulb over the head at the time of emergence of an interesting thought is not so far from the truth.