...Making precise comparisons to earlier periods can be difficult: Some income and wealth numbers are estimates, and income is only one way of measuring wealth. Still, there are some notable ways to measure gilded ages.

In the late 1890s, when the average American worker’s weekly wage was less than $10, John D. Rockefeller was earning about $192,000 a week. When he died in 1937, the estimated annual investment return on his $1.4 billion wealth produced an income equal to that of about 116,000 American workers, according to Branko Milanovic, lead economist for the World Bank research group and the author of “The Haves and the Have-Nots.” Today, Bill Gates’s annual income equals that of about 75,000 workers.

“If you compare Rockefeller’s income and the average income in the United States, then the gap was even greater in those days,” Dr. Milanovic said. “In the 1920s, though, the overall distribution of income is about the same as now in terms of inequality — very high.”

J. Bradford DeLong, an economics professor at the University of California, Berkeley, largely agreed. “Because the economy was smaller back then, fewer people — John D. Rockefeller, Andrew Carnegie, J. P. Morgan — were more powerful in the country,” he said....