(_f_) A book-packet may contain any number of separate books or other publications (including printed or lithographed letters), photographs (when not on glass or in cases containing glass), prints, maps, or any quantity or quality of paper, parchment, or vellum. The whole of this description of paper, books, and other publications, may either be printed, written, engraved, lithographed, or plain, or the packet may consist of a mixture of any or all these varieties. The binding, mounting, or covering of books and rollers, &c. in the case of prints or maps, are allowed. In short, whatever usually appertains to the sort of articles described, or whatever is necessary for their safe transmission, may be forwarded through the post at the same rate charged for the articles themselves.
(_g_) Among the general restrictions, we find the following:--
No book-packet must exceed two feet in length, width, or depth.
No book-packet must contain anything inclosed which is sealed against inspection, nor must there be any letter inclosed, or anything in the way of writing in the packet of the nature of a communication, either separate or otherwise. Entries on the first page of a book, merely stating who sends it, are allowable (and even desirable in case of failure of delivery) inasmuch as they are not regarded as of the nature of a letter.
Any packets found with a communication written in it (if the communication in question cannot be taken out, but forms a component part of the packet) will be charged with the _unpaid letter postage_, and then sent forward.
If a packet be found containing an enclosure, whether sealed or otherwise, or anything of the shape of a letter, such enclosure or letter will be taken out and forwarded separately to the address given on the packet. It is sent forward, of course, as an unpaid letter, but, in addition, another single rate is charged. Thus, if the article taken out of the packet does not exceed half an ounce in weight, the charge of threepence will be levied on delivery, while the remainder of the packet, if prepaid, will be delivered free at the same time.
(_h_) And lastly. The conveyance of letters being the main business of the Post-Office, the authorities make distinct stipulations that book-packets and newspapers must not interfere with the quick and regular conveyance and delivery of letters. Though it is believed to be of very rare occurrence, head postmasters are authorized to delay forwarding any book-packet or newspaper for a period not exceeding twenty-four hours beyond the ordinary time, if the other interests of their office demands it.