Hi. Those of you familiar with the classic problem in Jackson, where a dielectric sphere (diel const = k) is placed in a uniform electric field E_0, may recall the simple expressions for the field inside of the sphere: E_in = 3/(2+k) E_out. The solution tells us that the field strength within the dielectric is reduced by a factor 3/(2+k). I am trying to find the corresponding reduction factor for a dielectric cube in place of the dielectric sphere. I suspect that the reduction factor is simply 1/k, since that what it is in 2 dimensions, but I'm not sure. Does anyone know what the reduction factor is, or where I can find it?