Show WHY ELECTRIC LIGHTS HISS due to the Heated carbon points evaporating prof sylvanus thompson lias been answering a question which has often puzzled the public the arc light proceeds from the points of two little carbou rods as large as ones little finger prof thompson explains what is the state of the carbon when the lamp is throwing out its light lie says reports the pittsburgh dispatch that the carbon is sometimes actually melting a thing that was until recently thought impossible moreover he says that when a light is hissing the liquid carbon is really boiling in ordinary combustion the state of the arc crater is such that the solid carbon below is covered with a layer or film of liquid carbon just boil ing or evaporating off when hissing takes place the new state of things is bet up he bays if you watch a short hissing arc you will see a column of light concentrating itself on a narrow spot and the spot keeps moving about and is very unstable in position as well as in the amount of light it gives out the crater surface after the arc has been hissing is found to be literally honeycombed when the arc is hissing you can see little bits erupted out and tho hissing seems to be compared to the hissing which takes place in boiling water there is in tact exactly the same kind of difference between the silent arc abid the hissing ore as between quiet evaporation and a noisy boiling |