Hill made the case that if letters were cheaper to send, people, including the poorer classes, would send more of them, thus eventually profits would go up. Proposing an adhesive stamp to indicate pre-payment of postage – with the first being the Penny Black – in 1840, the first year of Penny Post, the number of letters sent in the UK more than doubled. Within 10 years, it had doubled again. Within three years postage stamps were introduced in Switzerland and Brazil, a little later in the US, and by 1860, they were used in 90 countries.