http://mathworld.wolfram.com/LaplacesEquationSphericalCoordinates.html

http://www.math.ubc.ca/~dli/400potential1.pdf

http://people.maths.ox.ac.uk/trefethen/pdectb/laplace2.pdf

http://www.ee.ed.ac.uk/~afm/teaching/em3/3)%20potential/Laplace.ppt

http://www.math.northwestern.edu/~pgoerss/math360/laplacepde.pdf

http://www.luc.edu/faculty/dslavsk/courses/phys301/classnotes/laplacesequation.pdf