Conversation so far:
what happened to andrew carnegie in 1901?
Carnegie invested $40,000 in Story Farm on Oil Creek in Venango County, Pennsylvania.
In one year, the farm yielded over $1,000,000 in cash dividends.
what else happened in a year?
Carnegie worked with others in establishing a steel rolling mill, and steel production and control of industry became the source of his fortune.
was this a success?
I propose to take an income no greater than $50,000 per annum! Beyond this I need ever earn, make no effort to increase my fortune.
what else before?
Carnegie believed in using his fortune for others and doing more than making money.
what did he do?
Carnegie worked to develop several iron works, eventually forming the Keystone Bridge Works and the Union Ironworks, in Pittsburgh.
what was his greatest accomplishment?
Carnegie made his fortune in the steel industry, controlling the most extensive integrated iron and steel operations ever owned by an individual in the United States.
what is the most important fact mentioned in the article?
One of his two great innovations was in the cheap and efficient mass production of steel by adopting and adapting the Bessemer process.

Question: and what else?
Self-contained rewrite: What was Andrew Carnegie's great innovation other than adopting the Bessemer process?