[Electric engineering.] . pig. Fig. 3. 4. Direction of Current.—The shapeof the carbon points depends on the direc-tion in which the current flows. In Fig. 1,the top carbon is supposed to be thepositive one, so that the current flowsfrom the top to the bottom, as is nearlyalways the case in practice. Fig. 3 showsa section of the carbons, and it will benoticed that the upper or positive one be-comes hollowed out slightly, as shown at a,while the lower one becomes pointed. Thehollow a is known as the crater, and isthe seat of the greater part of the lightgiven out by the arc. When the arc is
[Electric engineering.] . pig. Fig. 3. 4. Direction of Current.—The shapeof the carbon points depends on the direc-tion in which the current flows. In Fig. 1,the top carbon is supposed to be thepositive one, so that the current flowsfrom the top to the bottom, as is nearlyalways the case in practice. Fig. 3 showsa section of the carbons, and it will benoticed that the upper or positive one be-comes hollowed out slightly, as shown at a,while the lower one becomes pointed. Thehollow a is known as the crater, and isthe seat of the greater part of the lightgiven out by the arc. When the arc is in 4 ELECTRIC LIGHTING. § 18 operation, the carbon becomes volatilized at the crater, andthis vapor of carbon conducts the current to the negative car-bon. Although the temperature of the negative carbon ishigh, it is not nearly so high as that of the vapor and,hence, the latter is condensed on the negative tip formingthe point or else is thrown off. Only a portion of the vaporis so condensed; part of it combines with the oxyg
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