By 1880, both Edison and British physicist Joseph Swan had applied for patents on which type of electric lamp?

By 1851, which American photographer's failing eyesight had begun to hamper his work? By 1857, who was producing 10,000 steel plows a year? By 1871, which was the largest kingdom in the German Empire? By 1877, which author had his idea for a story in which Edward VI and a poor boy change places? Which inventor set up his famous research laboratory in Menlo Park, New Jersey, in 1876? Which wealthy New York family's fortune began with the fur trade and Manhattan real estate amassed by its German-born f… By 1890, the Scott brothers of Philadelphia sold more of which paper product in the U.S. than any other company? Which Russian author and playwright wrote hundreds of short stories, including "The Steppe"?