For many years it had been observed that a peculiar light was seen sometimes in the mercurial barometer, but Hauksbee and the other scientific investigators supposed the radiance to be due to the mercury in a vacuum, brought about, perhaps, by some agitation.

That this light might have any connection with electricity did not, at first, occur to Hauksbee any more than it had to his predecessors.

The problem that interested him was whether the vacuum in the tube of the barometer was essential to the light; and in experimenting to determine this, he invented his "mercurial fountain." Having exhausted the air in a receiver containing some mercury, he found that by allowing air to rush through the mercury the metal became a jet thrown in all directions against the sides of the vessel, making a great, flaming shower, "like flashes of lightning," as he said.

But it seemed to him that there was a difference between this light and the glow noted in the barometer.

This was a bright light, whereas the barometer light was only a glow.