The electric egg demonstrates electrical phenomena in gases at various pressures. The wooden base of this egg would be unscrewed, and the brass valve at the bottom would be screwed onto a vacuum-pump. Air would be pumped out of the glass tube, and electricity delivered to the upper electrode. At very low pressures, the inner air starts to glow and as the pressure increases the glow would change. Eventually sparks would form, and as pressure increases to normal, the electricity acts as normal. C. 50cm height.