332 
MRS. H. AYRTON OX THE MECHANISM OF THE ELECTRIC ARC. 
frequencies, and that for two cored carbons, which starts highest, must also cut the 
other two, so that the curves will be like I (fig. 14), if the curve starts lower when 
Fig. 14. Suggested curves connecting SV/SA with the frequency of the superimposed alternating current 
for a constant direct current and length of arc. 
the positive alone is cored, than when the negative alone is cored; and like II 
(fig. 14) if it starts higher. 
The Effect Produced by Coring Either or Both Carbons on the Curve Connecting the 
Non-Normal Value of SV/SA with A, when the Length of the Arc is Constant. 
Take next the curves connecting SA 7 /BA with the normal direct current, when the 
length of the arc and the frequency of the alternating current are constant. 
In Tables V. and VI., pp. 327, 328, the cross-section ratios for solid carbons differ 
less, on the whole, from the corresponding current ratios the larger the current on which 
the increase of 2 amperes has been superimposed. This shows that with solid carbons, 
when the length of the arc is constant, SA" SA diminishes as the current increases. 
Consequently the curve connecting S\" SA with A for solid carbons is of the form 
ABC (fig. 15). AVith cored carbons the curves depend not only on SAT/A, which 
is obtained from Tables A 7 , and A 7 I., but also on SAy/SA, the curves connecting which 
with A are given in fig. 13. The curves connecting SV r /SA with A cannot be obtained 
straight from Tables A", and VI., because the values are too irregular, but we can 
