igii.] 



WHITEHEAD— HIGH VOLTAGE CORONA IN AIR. 



383 



and built up by soldering with a line blow flame so that the strands 

 were uniformly tangent to each other throughout. The results indi- 

 cate the further lowering of the critical voltage when spiralling is 

 absent. The ratio c/a falls from .71 for the spiralled three-strand 

 to .61, and the difference for the four-strand is somewhat greater. 

 The pitch of the spirals of the cables investigated does not appear 

 to follow any regular rule. This irregularity however does not 

 appear to have any corresponding effect on the points of the curve 



o 



^- 



Number or Strands. 

 Fig. 4. 



of Fig. 4. From this it may be concluded that for a pitch of spiral 

 less than twelve diameters there is no gain on the ground of lessened 

 surface intensity due to the more uniform distribution of the elec- 

 tric field. 



At this writing the author has been unable to obtain solutions of 

 Levi-Civita's expression as applied to three and four strands. These 

 would permit by the foregoing results a knowledge as to how the 

 maximum corona intensity for a round wire compares with that 



