In this paper we use the term 'physical tensor' to stand for a tensor that
belongs to a tensor subspace. Based on the relationship among the character
s of rotation representation, some techniques are developed in order to giv
e the numbers of independent deviatoric tensors contained in the irreducibl
e decompositions of physical tensors, even prior to the constructions of th
e irreducible decompositions. A number of examples are shown and many of th
em are new results.