A. D. Smith, The Development of Rates of Postage…
“ Merchants' and manufacturers' samples are not, of course, strictly speaking, of the nature of correspondence, and their conveyance by post represents in some aspects an expansion of function. The main function of the Post Office is the distribution of letters, or, as it may be expressed generally, the distribution of any species of communication between persons, reduced to material form, whether as manuscript letters, postcards or circular letters, printed or written, or even in the form of newspapers. ”
