Oliver Heaviside Wrote Maxwell’s Equations (2013)(theinstitute.ieee.org)

   Norbert Wiener in 1926:

    "The brilliant work of Heaviside is purely heuristic,
    devoid of even the pretense to mathematical rigor. Its
    operators apply to electric voltages and currents,
    which may be discontinuous and certainly need not be
    analytic. For example, the favorite corpus vile on
    which he tries out his operators is a function which 
    vanishes to the left of the origin and is 1 to the 
    right. This excludes any direct application of the 
    methods of Pincherle…
    Although Heaviside’s developments have not been 
    justified by the present state of the purely 
    mathematical theory of operators, there is a great deal 
    of what we may call experimental evidence of their 
    validity, and they are very valuable to the electrical 
    engineers. There are cases, however, where they lead to 
    ambiguous or contradictory results..."