906 Prof. Wood and Mr. Hemsalech on Fluo 



re see nee 



jet, yet only the " water-band" streamer shows below and 

 above the moving gas stream. In fig. 7 the nitrogen was 

 flowing out of the tube at a much higher velocity, and the 

 luminosity is very much less, i. e. we are beginning to get the 

 effect shown by the water-band streamer with lower velocities; 

 The nitrogen in the jet-chamber was evidently set in violent 

 motion by the high velocity current, and the displaced nitro- 

 gen bands are visible as complete streamers, instead of being 

 localized in the moving current as in figs. 5 and 6. We 

 next tried blowing a strong current of nitrogen down against 

 the jet, from a tube inserted in the top of the jet-chamber. 

 Its effect is shown by fig. 8. The water-band streamer is 

 greatly weakened and the nitrogen streamers run up still 

 higher, being almost as intense at the top of the picture 

 where the nitrogen is in rapid motion, as at the bottom where 

 the movement is less violent. 



In all cases we found that the time of exposure necessary 

 to record the fluorescent bands of nitrogen could be enor- 

 mously reduced by keeping the gas in motion. It seems 

 much as if there was a fatigue effect, a flash of fluorescence 

 resulting from the spark radiations, followed by an inability 

 to respond to the radiations from subsequent sparks. It will 

 be remembered that precisely the opposite effect was found 

 for the "water-bands" which disappear entirely if the gas is 

 in rapid motion. 



Many experiments have been made to determine the origin 

 of the water-bands. They appeared much stronger in our 

 nitrogen gas than in air, but it must be remembered that our 

 nitrogen contained oxygen. We found, however, that if we 

 added more oxygen to the nitrogen the water-bands were 

 reduced in intensity. If the jet-chamber was filled with 

 oxygen the water-band streamer was exceedingly faint, 

 perhaps ^o °f the intensity which it had in the case of the 

 nitrogen, and no other streamers were visible. A current 

 of coal-gas gave the double band shown in fig, 9. 



If a moving stream of oxygen is directed across the jet y 

 the jet-chamber being open on both sides and filled with air, 

 that portion of the water-band streamer which is crossed by 

 the oxygen stream disappears, while a displaced band appears- 

 in the same position as the nitrogen band, only much fainter 

 (fig. 10, PL XIV). Yie might attribute this to an impurity 

 of nitrogen in the oxygen, brought out by having the gas in 

 motion, but we must remember that a moving current of air 

 gives no trace of any displaced band. It is quite probable 

 that impurities present in the gases or derived from the 

 rubber tubes through which they passed are responsible for 



