‎"HERSCHEL, J.F.W. (JOHN FREDERICK WILLIAM). - THE ""HERSCHEL CONDITION"" INTRODUCED.‎
‎On the aberration of compound lenses and object-glasses. Read March 22, 1821.‎

‎London, W. Bulmer and W. Nicol, 1821. 4to. No wrappers as extracted from ""Philosophical Transactions"" 1821 - Part I. With titlepage to Part I. Pp. 222-267 a. 1 engraved plate. Verso of titlepage with 2 stamps.‎

Reference : 46100

‎First appearance of this importent paper in optical theory in which Herschel described how to free lenses from the aberration for two axis points, one of which is infinitely distant. It is known as Herschel's condition. ""Sir John Herschel gave the condition which must be satisfied in order that a symmetrical optical system, free from spherical aberration for two conjugate axial points, may also be free from spherical aberration for two neighbouring and conjugate points upon the axis of the system" but Herschel's condition applies only to first order aberration, i.e. to aberration depending upon the cube of the inclination of the ray to the axis. Abbe shewed, later, that this condition could be included in a wider result, viz. that the spherical aberration, supposed zero, is stationary for axial variations provided that the incident and emergent rays for two conjugate axial points, associated with modified magnification m, satisfy the relation. (G.C. Stewart)‎