Edison's lamp - A drawing of a light bulb on a piece of paper

The first glow lamp which T. A. Edison constructed had platinum wire, similar to the one devised by Changy. Edison examined the properties of many organic and inorganic substances, with a view of finding the best substance for the filament, and fixed finally upon bamboo fibre.

By means of machinery the bamboo is divided into fibres of i millimetre in diameter, and 12 centimetres in length. These fibres are pressed into U-shaped moulds, which are put by thousands into ovens, where they are allowed to become carbonised. The carbon filament is attached to platinum wires, which are fused in a glass vessel having the form shown in Fig. 431. The vessels are exhausted by air-pumps, constructed by Edison for the purpose. During exhaustion an electric current is sent through the carbon filament, for the purpose of driving off any gases which might have been absorbed by the carbon. To prevent the platinum wires from melting at high temperature, the carbon filaments are considerably thicker at the end connected with the platinum wires, so as to offer less resistance to the current. (text continues on fig. 432)