Moon and Spencer, Field Theory Handbook The 2D "Maxwell curves" Fig. 2.10 (page 65) can be used to give an analytic approximation so long as the spacing is smaller than the radius. This is a conformal mapping onto parallel plates: z = (a/pi) (w + 1 + exp(w)) where the plate spacing is 2a The original publication was Springer-Verlag 1961, a republication was done by Springer in the 1980s. Many of the books by Moon and Spencer (Parry Moon and Domina Eberle Spencer) have excellent material on analytic, closed form solutions for various geometries. This is also shown in Fig 12.04 and equation 12.10 in Moon and Spencer Field Theory for Engineers, D. van Nostrand Company, 1961 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu