Recently I reorganized and greatly expanded my discussion
of the definition of capacitance and the procedures for
calculating capacitance matrices. I decided to give it
its own web page: http://www.av8n.com/physics/capacitance.htm
Note that formerly this was just a subsection of the page
on solving Laplace's equation numerically using spreadsheets: http://www.av8n.com/physics/laplace.htm
Keeping these two topics separate seems to be an improvement.
Let me know if there are any questions, suggestions, et cetera.