  This article shows the relation between the inertial mass and the gravity
mass. The gravity field can propagate only with a limited velocity. Therefore
the Helmholz equation is introduced for the gravity potential. The analysis of
the Helmholz equation leads to the "Maxwell equations" for the gravity field.
The dualism between the electricity and the gravity shows that the structure of
the own gravity field of a mass object is responsible for his inertial mass.
Additional all dual electric field values are described in the gravity field
notation.
