This Historical Summary, compiled by Mr. Lang, was originally contained in a Letter addressed to the Secretary to the General Post Office in Scotland, with a view to its being included in the Annual Report of the Postmaster-General, presented to both Houses of Parliament at the commencement of the present Session, but it not being considered necessary to include the whole Summary in the Report, Extracts only were published in the Appendix. The whole Summary is therefore now printed, with his Grace's sanction, for private distribution.

You can download it here in pdf format

See also...

The Royal Mail
Its Curiosities and Romance by James Wilson Hyde, Superintendent in the General Post Office, Edinburgh (second edition) (1885) (pdf)