The process employed consists essentially in first solidifying the least volatile part of the air and then causing it to evaporate with extreme slowness.

A tube with electrodes enables the spectrum of the gas in process of distillation to be observed.

In this manner, the spectra of the various gases may be seen following one another in the inverse order of their volatility.

All these gases are monoatomic, like mercury; that is to say, they are in the most simple state, they possess no internal molecular energy (unless it is that which heat is capable of supplying), and they even seem to have no chemical energy.

Everything leads to the belief that they show the existence on the earth of an earlier state of things now vanished.