A two-dimensional field of flow which is both divergenceless and
irrotational can be characterized by either one of the scalar
functions 
or 
. This type of flow, which bears the
name of Laplace, possesses a number of interesting features
which have been extensively investigated, and forms the
bulk of much of the classical literature on the subject of
hydrodynamics. Only some of the properties of this type of flow
will be dealt with here. For a more exhaustive treatment, the
reader is referred to the incomparable work of Lamb.