the Occurrence of Enhanced Lines in the Arc. 837 



They are strongly emitted throughout the arc flash, though 

 slightly enhanced and symmetrically widened in the first 

 phase ; hence these lines appear to be sensitive to the intense 

 electric actions o£ which the liquid film is the seat. This 

 observation is therefore quite in keeping with the known 

 behaviour of the triplets in the single plate resistance 

 furnace. 



The lines of the Rydberg series, which form the third type, 

 are hardly visible in the layer of paraffin oil though very 

 intense in the water and glycerin films. A special character 

 of these lines is their tendency to expand towards the red. 

 The wings thus formed are particularly well developed in 

 the water film ; but they also remain a prominent feature 

 during part of the second phase of both the water and 

 glycerin arcs, and, what must be considered a significant 

 event, they disappear abruptly, the emission continuing as 

 narrow symmetrical lines till the cessation of the luminous 

 phenomenon. In the paraffin-oil arc the third type lines 

 attain their maximum of development only towards the end 

 of the second phase. From these few results it is, however, 

 difficult to derive any definite conclusions as to their origin 

 or mode of excitation under these particular condition s> and, 

 ■although, we feel inclined to assign their emission in the main 

 to electric forces, their great feebleness in the paraffin-oil 

 film seems to point to the necessity of concurrent chemical 

 actions. 



With regard to the snark lines, these form a most pro- 

 minent feature of the spectrum emitted during the film stage 

 with all three liquids. In particular the line A. 4481 shows an 

 extraordinary development and, as regards relative intensity 

 and width, approaches its characteristic appearance in a 

 capacity spark. The symmetrical broadening of this line 

 is greatest in the water film. During the second phase 

 its breadth diminishes very rapidly and, at a definite moment,- 

 its intensity falls off quite abruptly, the line continuing as a 

 narrow and feeble one. The abrupt drop in intensity of this 

 line, both in the water and glycerin arcs, occurs at the same 

 instant as the sudden disappearance of the red wings of the 

 third type lines, as though the radiating centres were at this 

 moment undergoing some profound modification in their 

 •constitution. 



The three liquids employed — namely, distilled water, 

 paraffin-oil, and glycerin, are bad conductors of electricity, 

 and it might therefore be contended that films of these 

 liquids placed between the poles act as dielectrics. That 

 this is, however, not the case was shown by placing a drop 



