What was the difference between men's and women's salary from 1880 to 1920?

What was the difference between men's and women's salary from 1880 to 1920?
1880 hours and 1920 hours represents a difference of one weeks leave (40 hours)... 1880 is a typical amount of work hours in one year for the federal government and it assumes four weekes of leave. Industry supporting government projects does not always provide its employees four weeks of leave. Generally its three causing the increase in available work hours. It is not a GENDER issue...