Let a function
f be nonconstant and meromorphic in a domain
D in the plane, and let
M(
f) be the set of points where the spherical derivative |
f'|/(1+|
f|
2) has local maxima. The components of
M(
f) are at most countable and each component is (i) an isolated point, (ii) a noncompact simple analytic arc terminating nowhere in
D, or, (iii) an analytic Jordan curve. Tangents to a component of type (ii) or (iii) are expressed by the argument of the Schwarzian derivative of
f. If Δ is the Jordan domain bounded by a component of type (iii) and if Δ⊂
D, then the spherical area of the Riemann surface
f(Δ) can be expressed by the total number of the zeros and poles of
f' in Δ. Solutions of a nonlinear partial differential equation will be considered in connection with the spherical derivative.
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