Page:Proceedings of the Royal Society of London Vol 69.djvu/427

Rh and when the hydrogen became visible the first line to appear was the red.

That the change from parti-coloured stratifications to all pink is occasioned by an alteration in the intensity of the spark, is also shown by the fact that altering the make and break of the coil produces the same change as putting in the water resistance. Screwing up the hammer-spring so as to induce strong magnetism in the core and high potential of spark, gives pink and blue parti-coloured buttons. Weakening the spring, and thus weakening the magnetism, gives buttons which are all pink. I cannot, however, in this way cause the migration of the blue buttons to one single button in front. This phenomenon is produced only by an alteration of the exhaustion. Conversely, an alteration of the exhaustion will not change parti-coloured buttons to buttons of all one colour ; this requires a change in electrical energy.

I consider the water resistance acts thus : At the same rarefaction, hydrogen conducts the current better than mercury vapour. With a strong induction-spark at a certain degree of exhaustion, the conducting power of the rarefied hydrogen is not sufficient to carry the whole of the current ; some of it, therefore, is conducted through the mercury vapour, when the intensity of the blue drowns the feebler colour of the hydrogen. When, however, a resistance of 6 inches of water (equal to about 500,000 ohms) is inserted, the current is so weakened that the hydrogen can carry the whole of it, and the blue of the mercury is not seen.

The phenomenon of blue faces on the pink discs is probably due to some such action as the following : At the exhaustion necessary to give stratifications, there is a wide dark space round the negative pole. Here the negative electrons (Radiant Matter), issuing from the pole with enormous velocity, have sufficient energy to clear a space in front of them to a distance varying with the degree of exhaustion.

Dr. A. Schuster considers that the discharge through mercury vapour in a vacuum tube, when quite free from air, will not give rise to stratifications, nor to the dark negative space. My own experiments show that the dark space will form in pure mercury vapour. Whichever view may be correct, there is no doubt that if stratifications in mercury vapour are not altogether unknown, they are much more difficult to produce than similar phenomena in hydrogen or other diatomic gases. At a certain critical stage of the exhaustion, when