Feynman, R, Leighton, R, and Sands, M（1970）．“Chapter 12: Electrostatic Analogs”，The Feynman Lectures on Physics．Addison-Wesley-Longman． Gilbarg, D and Trudinger, N（2001）．Elliptic partial differential equations of second order．Springer．ISBN 978-3540411604． Schey, H. M.（1996）．Div, grad, curl, and all that．W W Norton & Company．ISBN 978-0393969979．
Feynman, R, Leighton, R, and Sands, M（1970）．“Chapter 12: Electrostatic Analogs”，The Feynman Lectures on Physics．Addison-Wesley-Longman． Gilbarg, D and Trudinger, N（2001）．Elliptic partial differential equations of second order．Springer．ISBN 978-3540411604． Schey, H. M.（1996）．Div, grad, curl, and all that．W W Norton & Company．ISBN 978-0393969979．