What was the systematic technique Herschel employed to map the three-dimensional structure of the Milky Way?

Answer

Star gauging

Star gauging involved counting stars within small, uniform patches of the sky to deduce the overall density and shape of the stellar system surrounding the Sun.

What was the systematic technique Herschel employed to map the three-dimensional structure of the Milky Way?
astronomyUranustelescopeAstronomerdiscoveries