Page:Proceedings of the Royal Society of London Vol 69.djvu/428

410 both hydrogen and mercury are present, I obtain both mercury and hydrogen strata.

The following experiments appear to show that the presence of hydrogen* has a considerable influence on the behaviour of mercury vapour in vacuum tubes. A tube with aluminium terminals had been attached to the pump for several days, and consequently mercury had diffused in and condensed on its sides. The tube was exhausted until, under the electric discharge, it phosphoresced of a brilliant green and Avas near the non-conducting point. It was heated very strongly with a Bunsen flame, when a faint pink luminosity was observed between the poles, the spectrum of mercury being absent. The tube was allowed to cool and a little hydrogen was introduced, when the usual pink stratifications appeared. On heating the tube to about the same tem- perature as before blue faces showed on the pink buttons, and the mercury spectrum was seen throughout the tube, especially in the neighbourhood of the negative pole.

It is known that in a vacuum tube, at an exhaustion approaching the stratification-point, any slight obstruction, such as constriction in the tube, or a series of wires sealed in, will cause luminous strata to hang round the obstruction. In a similar way, the hydrogen strata afford an anchorage, as it were, for the mercury, each hydrogen lumi- nosity having a little blue glow of mercury hanging on to it ; whereas, were there no hydrogen, no mercury stratifications would be seen.

The pink- and blue luminosities show where the electrons and gaseous atoms meet ; when the speed of the electrons is suddenly diminished, the shock throws the atom into greater vibration, which, being communicated to the ether, produces vibrations of definite wave- lengths, constituting the special spectrum of the atom. The dense mercury atom is not driven back so much as the lighter hydrogen atom hence the blue front to the pink buttons. A very little dif- ference in the exhaustion suffices to break the adhesion between the mercury and the hydrogen ; then the mercury vapour diffusing along the tube meets the electrons from the negative pole and is swept back to the head of the hydrogen strata, and becomes apparent as a single button of blue light.

I have spoken of " Radiant Matter " and " Electrons " as if they were identical. Nearly twenty-five years ago I was led by experi- ments in highly rarefied tubes to assume the existence of matter- in an ultra-gaseous state. Later, in a lecture delivered before the British Association at the Sheffield Meeting, 1879,f I first used the

instance the hydrogen generator was attached to the tube. t ' Chemical News,' vol. 40, pp. 91, 104, 127.
 * Possibly another gas would do as well. Hydrogen was used because in this