of the permittivity 
of the material to the permittivity of free space 
[P3.3, P4.5]
of: a material
is: the dimensionless ratio of the permittivity of the material to the permittivity of free space [P3.3, P4.5]
is therefore: the factor by which the electric field strength due to an arbitrary charge distribution is reduced in the medium compared with its value in free space. [P3.3]
Copyright 1997, The Open University