The paper says:

Third, the mass of Jupiter, if distributed in a spherical shell revolving around the sun at twice the Earth's distance from it, would have a thickness such that the mass is 200 grams per square centimeter of surface area ( 2 to 3 meters, depending on the density). A shell of this thickness could be made comfortably habitable, and could contain all the machinery re-quired for exploiting the solar radiation falling onto it from the inside.