All About Inventions and Discoveries
The Romance of modern scientific and mechanical Achievements

22Ö All About Inventions commercial approval. As a result of further experi- ment, he evolved an improved filament consisting of carbonised parchmentised cotton-thread, and this he shaped in a loop capable of being placed within a pear-shaped, spherical, or any other form of bulb, and wherein, owing to the terminals of the loops coming side by side in the holder, it was possible to introduce the lamp in any way—hanging or standing vertically, at an angle, or in any other desired position —into an electric wiring circuit. Swan carried out his work in the secrecy of his laboratory. He apparently did not court publicity, and little seems to have leaked out concerning what he was doing or what he had accomplished. In 1877 —seventeen years after Swan had solved the problem —the American inventor, Thomas A. Edison, attacked the question. He certainly appears to have been entirely ignorant of what the British inventor had already accomplished, or if he had heard of his work, he invested the reports with very slender significance, owing to the little information thereof which was available, because he commenced his researches with carbonised paper, to discover what Swan had ascer- tained long before. Edison, however, was facilitated by an invention which had been introduced to the world in 1865, and which had been denied to Swan in his earlier days. This was the Sprengel air-pump, which offered a means to obtain an extremely high vacuum in a glass globe. This air-pump induced Edison to revert to the carbonised cotton thread which Swan had used, and which Edison also deter- mined to be the most promising substance for this* purpose after testing a wide range of other materials.