We prove in this paper that any maximal, with respect to inclusion, subset of N – the family of all increasing sequences of positive integers –
possessing the harmonic series property has the cardinality of the continuum.
Moreover, we prove that for any countable (infinite) set
exists an "orthogonal" family such that it hold some facts. All facts are proved constructively, by using the modified version of the classical Sierpiński family of increasing sequences having the cardinality of the continuum.