the Occurrence of Enhanced Lines in the Arc, 849 



them so as to retard arcing. As long as B is in contact 

 with A on striking the arc, the intensity of the field between 

 them is of course zero. But immediately after separation 

 as B moves upwards, a very strong electric field is set up, 

 the intensity of which, however, decreases very rapidly 

 as the distance between A and B increases, and more espe- 

 cially so as soon as arcing has set in after the destruction of 

 the liquid film. Hence we should expect to observe the 

 electric effect whilst the distance between B and A is small, 

 as for example during the first phase. An image of the 

 arc flash composed of the two phases was projected upon 

 the slit of the spectrograph in such a manner that the motion 

 of B took place in a direction parallel to the slit. In this 

 way it was possible to distinguish between the spectrum 

 radiations emitted during the first phase and those given out 

 at later stages of the arc flash. The height of the spectrum 

 thus obtained obviously depends upon the distance AB, 

 namely the length of the arc flash, and that edge of the 

 spectrum which corresponds to the vicinity of A will be 

 emitted whilst the intensity of the electric field is a maximum. 

 We should therefore, on passing down a spectrum line from B 

 towards A, observe a broadening or decomposition of the line 

 analogous to that obtained with Lo Surdo ? s arrangement"*. 

 The liquids which were placed in the arc gap in our experi- 

 ments contained hydrogen in combination either with oxygen 

 or with carbon, and the spectra show the red and blue lines 

 of the Balmer series. The red line X 6563 was found to 

 broaden considerably near the edge of the spectrum corre- 

 sponding to electrode A. The blue line X4862 was, however, 

 distinctly decomposed in the first phase, the distance between 

 the components increasing on approaching A ; in fact, this 

 line presented the well-known Eiffel tower-like appearance, 

 so characteristic of the transverse electric effect, as obtained 

 with Lo Surdo's method. The effect is especially well 

 developed and defined in a 200 volt arc between copper or 

 magnesium poles with water films. It shows also in hydrogen 

 and coal-gas. The fact that H a was only broadened and not 

 decomposed is undoubtedly due to the low dispersion in the 

 red of the glass-prism spectrograph used by us. With 

 the help of Stark's table of data for " Grobzerlegung " + an 

 approximate determination of the intensity of the electric 

 field was made from the amount of maximum separation 



* Lo Surdo, Rendiconti del Lincei, xxii. p. 664 (1913). 

 + Usabura Yoshida, Memoirs of the College of Science (Kyoto Im- 

 perial University) vol. iv. No. 5, p. 188 (1920). 



Phil. Mag. S. 6. Vol. 43. No. 257. May 1922. 3 I 



