Columbia subject headings:
Copper mines and mining--Technological innovations--United States.
Household appliances--Technological innovations--United States.
Labor supply--Effect of technological innovations on--United States.
Shipping--Technological innovations--United States.
Harvard subject headings:
Copper mines and mining--Technological innovations--United States.
Copper ores--Technological innovations--United States.
Household appliances--Technological innovations--United States.
Labor supply--Effect of technological innovations on--United States.
Shipping--Technological innovations--United States.
Princeton subject headings:
Copper mines and mining--Technological innovations--United States.
Household appliances--Technological innovations--United States.
Labor supply--Effect of technological innovations on--United States.
Shipping--Technological innovations--United States.