John Munro

The Story of Electricity John Munro

Book Excerpt: ...o a distance of several hundred yards, and thus took an important step in the direction of the electric telegraph. It has since been found that FRICTIONAL ELECTRICITY APPEARS ONLY ON THE EXTERNAL SURFACE OF CONDUCTORS. This is well shown by a device of Faraday resembling a small butterfly net insulated by a glass handle (fig. 5). If the net be charged it is found that the electrification is only outside, and if it be suddenly drawn outside in, as shown by the dotted line, the electrification is still found outside, proving that the charge has shifted from the inner to the outer surface. In the same way if a hollow conductor is charged with electricity, none is discoverable in the interior. Moreover, its distribution on the exterior is influenced by the shape of the outer surface. On a sphere or ball it is evenly distributed all round, but it accumulates on sharp edges or corners, and most of all on points, from which it is easily discharged. A neutral body can, as we have seen (fig. 4), be charged by...