BASQUIN. — THE ARC SPECTRUM OP HYDROGEN. 



173 



shown in the diagram. The dynamo furnishes a direct current of 110 

 volts, and when the switch was closed the current simply passed through 

 the arc and the resistance in series. The arc was stationary, one 

 electrode was carbon and the other a zinc rod. The induction coil used 

 is a duplicate of the one designed by Professor Rowland to give a short 



SWITCH 



SPARK 



Figure 1. 



spark but a very powerful discharge ; an alternating current of 110 volts, 

 6 amperes, was run through the primary, without an interrupter. The 

 condenser used has a capacity of ^^^ microfarad. It will be noticed that 

 the spark can take place only by passing in succession the two gaps 

 marked " arc " and " spark." The spectroscope is adjusted to observe 

 phenomena at "arc" gap. 



In performing this experiment I first turned on the spark and set the 

 cross-hairs of the eyepiece of the 10-ft. concave grating upon the zinc 

 spark line at 5895, between the D lines of sodium. The spark was 

 turned off and the arc turned on. The spark lines no longer appeared, but 

 came out instantly when the spark was again started along with the arc ; 

 both arc and spark were now running through the gap marked " arc " 

 and the spectroscope showed both arc and spark lines. Now while both 

 currents were on, the arc current was turned off ; the arc spectrum dis- 

 appeared, but the spark spectrum persisted with apparently the same 

 intensity as before and without an interval of darkness. 



This experiment shows that the first suggestion is not true ; that the 

 arc spectrum is not characteristic of the condition of the gases in the arc, 

 and makes it highly probable that the electrical cause of radiation is 

 not zero. 



In order to test my second suggestion above, I short-circuited the 

 spark gap shown in Figure 1. The spark line appeared as before in the 

 spark, but disappeared as soon as the arc current was made ; the arc and 

 the spark discharges were both passing through the arc as before ; I had 



