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Coming of Electric Lighting 225 use ? Forthwith he started experimenting for him- self, and then he recognised that the question was by no means so simple to solve as it appeared at first sight. However, he was not to be turned from his line of investigation, and recurring difficulties only served to spur him on. Every conceivable medium capable of being raised to incandescence under the passage of the electric current was tested, and a tangible idea of the laborious character of this particular quest may be gathered from the fact that fifteen years were expended upon the work before a practical incandescent lamp was obtained. As a result of the hundreds of experiments which were made Mr. Swan discovered that a fine thread of carbon of high resistance, when enclosed in a glass bulb from which the air had been exhausted, gave the most successful results, and he demonstrated the success of his experiments to a few favoured friends. This was in i860, and the carbon incandescent lamp did not differ very materially from that of to-day. The fundamental principle was the same, except that instead of the carbon being placed in the form of a loop within a pear-shaped bulb, it was carried through from end to end of an attenuated cigar-shaped tube. In the first successful lamps the carbon filament com- prised a strip of carbonised paper, and the lamp of this type is shown in the photograph facing page 224. This initial success prompted Swan to pursue his investigations. With the cigar-shaped tube he had succeeded in obtaining incandescent electric lighting. Now the issue was resolved into the modification of this principle into a form which should command p