Hittorf examined the phenomena exhibited in so-called high vacua, that is, in exceedingly rarefied gases.

This phenomenon is connected with the fact that incandescent bodies, especially in rarefied gases, throw off or emit electrons or gaseous negative ions.

But to the man of ordinary understanding, unused to the rarefied atmosphere of abstract thought, this conception of a transcendental, impersonal Spirit and the unreality of the phenomenal world can have no meaning: what he requires is a deity that stands in intimate relation to things material and to all that affects man's life.

There he continued his researches on the discharge of electricity in rarefied gases, only just missing the discovery of the X-rays described by W.

Earlier still the sun must have reached to where Neptune now revolves on the confines of our system, but the mass of the sun could not undergo an expansion so prodigious without being made vastly more rarefied than at present, and hence we are led by this mode of reasoning to the conception of the primaeval nebula from which our system has originated.