"In the manufacture of incandescent lamps the filament is connected to bits of metal called the 'leading-in' conductors. By means of these little pieces of wire the filament within the sealed glass globe is connected with the outside circuit-wires. To maintain a stable vacuum it has been found best to make the leading-in wires of platinum, since its coefficient of expansion is so nearly the same as that of glass that less trouble is caused by its expansion and contraction than is experienced with other metals. It has been the usual practice to introduce the platinum leading-in wires into a glass tube, and then to fuse and compress the tube around the wires in this manner, tightly sealing them into the glass. These wires have necessarily been of a considerable size, not for electrical reasons but for mechanical reasons, since they are required to support the filament, and to be of such rigidity that they will not be bent by the weight of the filament or by jarring. Of late, however, platinum has advanced very materially in price, and manufacturers are endeavoring to provide a substitute for the metal, or a means by which the amount used in a lamp may be reduced to a minimum. With this object in view Mr. Edison has devised the arrangement of leading-in conductors illustrated in the cut.

"Wires of copper, iron, nickel, silver and other metals, and some alloys having a greater coefficient of expansion than platinum, can be sealed into the glass; but on cooling, although they will still be held mechanically rigid by the glass, they contract sufficiently to permit air to pass into the vacuum. The peculiar feature of Mr. Edison's process is that leading-in wires of two metals are used, one section being of a metal having substantially the same coefficient of expansion as glass, such as platinum, the other being of a different and cheaper metal. Conductors thus formed of two metals are sealed into the glass, as shown in the illustration. The seal will remain perfect at the platinum sections, and it will, therefore, be immaterial if the copper or other wire contracts away from the glass."