This is a transpacific cover to New Bedford, Mass. from Hong Kong posted on 31 March 1877.

Hong Kong became a member of the General Postal Union (Later known as U.P.U.) in 1877 and on 1 April postage rate to member countries became 12c per half oz. (except via Brindisi to European countries and beyond when an extra 4c surcharge applied.)

Still franked with an 8c stamp which was the Anglo-american Convention rate. The sender probably did not read the Government Gazette in which the new U.P.U. (Actually called the G.P.U. at the time) rate was published a fortnight ago. Or perhaps, he did and sending the letter one day before thus saving himself 4c!

The Hong Kong PAID ALL c.d.s. was no longer necessary as a result of postal union membership.

However, since the Belgic did not leave Hong Kong few days after 1 April, should the post office charge the sender extra 4c? Apparently not since the letter was posted on 31 March.

It would be interesting to hear from anyone who has a F.D.C. of the new 12c or 16c rate; we do not want a "Fake Date Cover" however, even if 1 April is the Fool's day!