On July 24, 1874, Woodward and his partner, Matthew Evans, a hotel keeper, filed a Canadian patent application on an electric light bulb. It was granted on August 3, 1874 as Canadian patent number 3,738. Woodward was a medical student at the time. Their light bulb comprised a glass tube with a large piece of carbon connected to two wires. They filled the tube with inert nitrogen to get a longer burn life in the filament. Their light bulb was fully effective and sufficiently promising; they sold their U.S. Patent 181,613 to Thomas Edison. Thomas Edison obtained an exclusive license to the Canadian patent. Thomas Edison developed his own design of incandescent lamp with a high resistance thin filament of carbon in a high vacuum contained in a tightly sealed glass bulb which had a sufficiently long service life to be commercially practical.