68 



April i\th^ 1899. 



Mr. T. Workman, J. P., President, in the Ciiair. 



ELECTRIC DISCHARGES IN RAREFIED GASES, 

 WITH EXPERIMENTS AND LANTERN SLIDES. 



By J. FiNNF.GAN, B.A., B.Sc. 



The experiments on this subject have attracted the attention 

 of numerous observers, not only because of their beauty and 

 and variety, but also from the widespread belief that this is the 

 most promising field in which to discover the relationships 

 between electricity and matter. 



Consider the discharges in electrodeless tubes. Take a coil 

 of wire, of which one end is connected to the inside coating and 

 the other end through a spark gap to the outside coating of a 

 Leyden jar, charged by an induction coil. When the jar is 

 discharged enormous and very rapid alternating currents flow 

 through the coil, sufficient by their induction to produce 

 bright discharges in bulbs placed in the coil. If the bulb 

 is connected to pump and exhausted, when the pressure 

 is high no discharge appears, but when the pressure is 

 about imm. of mercury a thin red line runs round the bulb 

 in the plane of the coil ; continuing the exhaustion, the colour 

 changes to white, the ring gets thicker, and the brightness 

 becomes a maximum ; it then diminishes, and when we have a 

 very good vacuum the discharge no longer passes. If a metallic 

 diaphragm crosses the bulb there are produced two separate 

 bright rings, just as with a non-conducting diaphragm. 



There is always considerable difficulty in producing the first 



