300 
MRS. H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
To explain the further formation of the arc, we must remember that when the 
carbons are separated still more all the material in the gap cannot retain its high 
temperature. The access of the cold air must, I consider, turn some of the vapour 
into carbon mist or fog as distinct from carbon vapour , just as the steam issuing from 
a kettle is turned into visible mist at a short distance from its mouth. The interior 
globular portion A (fig. I), which is purple in the image of the arc, is, I suggest, 
composed of such carbon mist, while there is an indication of a space between 
Fig. 1. Enlarged image of arc and carbons with positive carbon on top. A A, pimple mist, 
BB, shadow, CC, green flame. 
this mist and the positive carbon which is occupied, I believe, by a thin film of true 
carbon vapour. 
Next the dissimilar action of the poles, met with in so many electric phenomena, 
begins. Instead of both poles volatilising, so that there is a thin layer of carbon 
vapour over each with a mass of carbon mist between them, the positive pole alone 
volatilises, while the negative appears simply to burn away. 
Besides the film of vapour and the bulb of mist, other volatile materials must go 
to make up the whole substance of the arc. For the surrounding air must not only 
cool the carbon vapour, hut it must unite chemically with a certain thickness of the 
mist, thus forming a sheath of burning gases surrounding both vapour and mist, and 
even portions of the solid carbons themselves. This sheath of gases, which is of a 
brilliant green colour with solid carbons, may be seen at C (fig. 1), while B, the 
shadow between it and the mist, probably indicates where the two mingle. There 
