of letters mailed. Before 1839, the number of letters sent in the United Kingdom was typically 76 million. By 1850, this increased five-fold to 350 million, continuing to grow rapidly until the end of the 20th century when newer methods of indicating the payment of postage reduced the use of stamps. Other countries soon followed the United Kingdom with their own stamps. The Canton of Zürich in Switzerland issued the Zurich 4 and 6 rappen on 1 March 1843. Although the Penny black could be used to send a letter less than half an ounce anywhere within the United Kingdom, the Swiss did not initially adopt that system, instead continuing to calculate mail rates based on distance to be delivered. Brazil issued the Bull's Eye stamp on 1 August 1843. Using the same printer used for the Penny black, Brazil opted for an abstract design instead of the portrait of Emperor Pedro II, so his image would not be disfigured by a postmark. In 1845, some postmasters in the United States issued their own stamps, but it was not until 1847 that the first official United States stamps were issued: 5 and 10 cent issues depicting Benjamin Franklin and George Washington. A few other countries issued stamps in the late 1840s. The famous Mauritius "Post Office" stamps were issued by Mauritius in September 1847. Many others, such as India, started their use in the 1850s, and by the 1860s most countries issued stamps. Perforation of postage stamps began in January 1854. The first officially perforated stamps were issued in February 1854. Stamps from Henry Archer's perforation trials were issued in the last few months of 1850; during the 1851 parliamentary session at the House of Commons of the United Kingdom; and finally in 1853/54 after the United Kingdom government paid Archer £4,000 for his machine and the patent. The Universal Postal Union, established in 1874, prescribed that nations shall only issue postage stamps according to the quantity of real use, and no living persons shall be taken as subjects. The latter rule lost its significance after World War I. The twentieth and twenty-first century After World War II, it became customary in some countries, especially small Arab nations, to issue postage stamps en masse as it was realized how profitable that was. During the 21st century, the amount of mail—and the use of postage stamps, accordingly—has reduced in the world