204 WEBER'S LECTURES cp läuft zw. 0 & 2n. ds: x = 0 y = R sin (p z = R cos (p m: x = X sin u y = X cos u z = 0 r = sJX2 sin2 u + (R sin (p - X cos u)2 + R2 cos2 (p = Jr2 + X2 - 2RX sin cp cos u = R /1 - 2 4- sin p cos u (bei Vernachlässigung R J " " X der 2. Potenz v - R = R ( 1 - ^ sin q cos u ).