  A simple geometric mechanism: "the locus of intersections of perpendicular
bisectors and normal lines", often arises in many guises in Nonlinear Sciences.
In this paper, a new application of this simple geometric mechanism is given.
Namely, we show that this mechanism gives answers to all four basic problems on
envelopes created by hyperplane families (existence problem, representation
problem, equivalence problem of definitions, uniqueness problem) at once.
