1885.] when raised to High Incandescence. 227 



Reversed the current through the filament. Returned to 90 volts, 

 and repeated the experiments! Filament current readings the same 

 as before, and also the blue effects. At 108 volts a slight blue effect 

 was noticed in the open end of the tube. 



Doubtless, if I could have increased the electromotive force, the 

 results would have been more marked ; but they were sufficient to 

 show that the effects were evident, even though the rarefied space 

 were greatly extended, as in the case of the tube attached to ]STo. 5 

 lamp. 



10. The tube was constructed so that no portion of the filament 

 was opposed by right lines to the metal plate (fig. 4) . 



Fig. 4. 



11. A lamp was constructed with three branches at right angles to 

 each other, as shown in fig. 5, and each metal plate taken in succession, 

 but no results were obtained. 



12. Professors Liveing and Dewar ("Proc. Roy. Soc," March 9, 

 1882) observed a " sort of flame " during high incandescence, show- 

 ing by its spectrum the presence of carbonic oxide. It was strongest 

 about the junction of the carbon thread and the positive electrode. It 

 was, according to them, the glow of the positive pole attending a 

 discharge in rarefied gas. 



It is a common thing with glow-lamps which have the heels of the 

 filament close together to have an arc forming across when the electro- 

 motive force at the terminals is too high. Hence in recent lamps 

 requiring 100 volts, Mr. Swan has considerably increased the distance 

 between the electrodes. Moreover, whenever the incandescence of 



