Page:Heroes of the telegraph (IA cu31924031222494).djvu/252

 hence the dynamo-electric generator, or 'dynamo,' was ere long invented and improved.

In 1878 the boulevards of Paris were lit by the arc lamps of Jablochkoff during the season of the Exhibition, and the display excited a widespread interest in the new mode of illumination. It was too brilliant for domestic use, however, and, as the lamps were connected one after another in the same circuit like pearls upon a string, the breakage of one would interrupt the current and extinguish them all but for special precautions. In short, the electric light was not yet 'subdivided.'

Edison, in common with others, turned his attention to the subject, and took up the neglected incandescent lamp. He improved it by reducing the rod of carbon to a mere filament of charcoal, having a comparatively high resistance and resembling a wire in its elasticity, without being so liable to fuse under the intense heat of the current. This he moulded into a loop, and mounted inside a pear-shaped bulb of glass. The bulb was then exhausted of its air to prevent the oxidation of the carbon, and the whole hermetically sealed. When a sufficient current was passed through the filament, it glowed with a dazzling lustre. It was not too bright or powerful for a room; it produced little heat, and absolutely no fumes. Moreover, it could be connected not in but across the main circuit of the current, and hence, if one should break, the others would continue glowing. Edison, in short, had 'subdivided' the electric light.

In October, 1878, he telegraphed the news to London and Paris, where, owing to his great reputation, it caused an immediate panic in the gas market. As time passed, and the new illuminant was backward in appearing, the shares recovered their old value. Edison was severely blamed for causing the disturbance;