Radiant Emission from the Spark. 711 



A plate of white fluorite, 0*5 mm. in thickness, which had 

 heen found very transparent for the Schumann waves by 

 Dr. Lyman, who very kindly placed it at my disposal, 

 together with an end-on hydrogen tube for the production of 

 Schumann waves, when placed over the aperture was found 

 to destroy all trace of the emission. This disposed of the 

 theory that we were dealing with a fluorescence produced by 

 the short waves. Thin aluminium foil, such as is used with 

 the Lenard tubes, was found to be equally opaque. It is 

 therefore a difficult matter to start the emission in a given 

 gas and pass it into a different one. The problem was finally 

 solved by an experiment designed to test one of the theories 

 that I had evolved to explain the phenomenon. It occurred 

 to me that we might be dealing with hydrogen ions, shot off 

 from the electrodes, which, by combination with the oxygen 

 of the air, gave rise to a spectrum similar to that of the oxy- 

 hydrogen flame. We might in this way explain the lessened 

 effect in oxygen as a result of the circumstance that the 

 " combustion " of the ions took place almost entirely within 

 the small tube with which the disk of aluminium was per- 

 forated. If this were the case, it seemed probable that if 

 the emission were formed in air, and a small jet of oxygen 

 were directed across it transversely, we should observe a 

 more intense action at the point where the emission met the 

 oxygen jet. The experiment was tried, and it was found 

 that the gas jet merely interrupted the emission, killed it in 

 other words, precisely as if it absorbed it. If the emission 

 was started in air and a jet of nitrogen blown gently against 

 the aperture, the emission was found to shoot out much 

 farther and to be of greater intensity. The magnetic field 

 appeared to be without action on it, though the experiment 

 was found to be attended with difficulties on account of the 

 action of the magnet on the spark. 



It is still more difficult to study the action of an electro- 

 static field. The material constituting the emission is 

 evidently shot from the aperture at a very high velocity, for 

 it is impossible to blow it aside with a strong jet of air ; 

 moreover, if air is forced continuously into the auxiliary 

 chamber, passing through the aperture in the aluminium 

 disk at a high velocity, the emission does not appear to be 

 held back in the slightest degree. 



I am unable to explain its reactions with oxygen and 

 nitrogen, and the apparent failure of the presence or absence 

 of water vapour to modify the intensity ot the spectrum, 

 which is made up chiefly of the so-called water-bands. 

 These bands appear when hydrogen burns in oxygen, and yet 



