In 1872, Alexander Lodygin decided to go to Saint Petersburg to attend lectures at Saint Petersburg Institute of Technology and to start working on an electrical helicopter (electrolyot). The helicopter would need some sort of artificial lighting. He decided to start his helicopter work by developing a source of electrical light for it, the filament lamp. For a filament, Lodygin used a very thin carbon rod, placed under a bell-glass. Soon he applied for a Russian patent for his filament lamp, he would also patent this invention in Austria, Britain, France, and Belgium. A year later, he demonstrated prototypes of his electric filament lamp in the physics lecture hall of the Saint Petersburg Institute of Technology. Although, he invented an incandescent light bulb before Thomas Edison, but it was not commercially profitable because in 1906 they were too expensive. Several of Lodygin's ideas were implemented much later, even after his death. In 1871 Lodygin proposed an autonomous diving apparatus that consisted of a steel mask, natural rubber costume, accumulator battery and a special apparatus for electrolysis of water. The diver was supposed to breathe the oxygen-hydrogen mix obtained by electrolysis of water. The invented diving apparatus was very similar to modern scuba equipment.