 Now performing a similar analysis for the heat transfer from surface "i" to surface "j",
where "R""ij" = 1/("A""i" "F""ij").Because the above is "between" surfaces, "R""ij" is the resistance of the space between the surfaces and "J"e,"i" − "J"e,"j" serves as the potential difference.Combining the surface elements and space elements, a circuit is formed.