Electrodeless Ring Discharge in certain Gases. 721 



diametral plane of the bulb and was vertical. The method 

 of getting the oscillatory discharge in this coil is shown in 

 the diagram. 



a, bj a\ b\ are the terminals of two leyden-jars, a', b being 

 connected to the secondary of a Cox induction-coil, and a, b\ 

 to an adjustable spark-gap S. To this spark-gap were 

 connected also the terminals of the coil D, which was placed 

 round the discharge-bulb B in the manner described. 

 Variations in the intensity of the discharge through D were 

 obtained by altering the frequency of the hammer-break of 

 the induction-coil, the length of the spark-gap, and the size 

 of the leyden-jars. In the experiments the spark-gap varied 

 between 2 and 15 mm., and the leyden-jars were usually 

 two gallon jars. 



The exhaustion of the bulb and the apparatus was carried 

 out by a Toepler mercury pump, and then by charcoal and 

 liquid air, exhaustion to a pressure below that at which any 

 discharge would pass being obtained in each case before the 

 admission of the gas to be examined. 



The observing spectroscope was a Hilger constant-deviation 

 instrument in which the wave-lengths of the lines observed 

 could be read directly from a graduated revolving drum. 

 In all cases the gases admitted to B had been dried by passing 

 through, and being left for some time in contact with, one 

 tube of calcium chloride and two tubes of phosphorus pent- 

 oxide, each about 50 cm. long. 



Method of Experiment 



When the discharge-bulb had been exhausted as above 

 some of the gas to be examined was admitted to the apparatus, 

 which was then gradually exhausted by liquid air and 

 charcoal until the highest pressure at which the true ring- 

 discharge would pass was reached. If the spectrum of the 

 discharge gave no indication of the presence of elements 

 other than those composing the gas under observation, the 

 pressure of the gas in the bulb was lowered gradually until 

 no discharge could be obtained, and the spectrum observed at 

 the different stages of this exhaustion. This process was then 



