The concept behind neon signs was first conceived in 1675, when the French astronomer Jean Picard observed a faint glow in a mercury barometer tube. When the tube was shaken a glow called barometric light occurred, but the cause of the light (static electricity) was not then understood.
Jean Picard is better known as the astronomer who first accurately measured the length of a degree of a meridian (longitude line) and from that computed the size of the Earth.
From -- where else? -- about.com
 When he wasn't manning the Starship Enterprise.