SINCE feudal days, subjects have hoped that petitioning the sovereign can have great effects. E-mail made writing to politicians easy. Now a new technology is making those missives public. Twitter messages (“tweets” in the jargon) are like public telegrams. No more than 140 characters in length, they can be sent from any computer or mobile phone. Anyone with an account (there are 100m and rising) can send a public message to anyone else by placing the @ sign before a username or a # sign before a topic.

That makes it much easier for voters to reach politicians and for politicians to react to them (or at least to pretend to). It helps election organisers too. At its height Barack Obama's campaign (@barackobama) employed 100 staff working on social media such as Twitter. But now it is catching on elsewhere. In July just four of the world's top 20 cities for Twitter use were outside America, according to HubSpot, a marketing firm. By January it had grown to eight.

Sebastián Piñera, the newly elected president of Chile, has asked all cabinet members to start tweeting. His own account is now the most-followed in the country. Venezuala's Hugo Chávez tweets too (@chavezcandanga). In June only three Japanese politicians had accounts; now Politter, a site dedicated to Twitter and Japanese politics, lists 485. An analysis of last year's German elections by the University of St Gallen discovered that 577 politicians had opened Twitter accounts, three-quarters of them in 2009. Greece's prime minister George Papandreou uses Twitter. But @primeministergr is the office, not the man. His staff tweet for him, sometimes using a code to signal who wrote what.

Twitter, says Mr Piñera's spokeswoman, Ena von Baer, means assessing reactions to announcements before presenting them in a press conference. But the scale of response makes it hard for office-holders to tweet themselves. Mr Obama reads just a select ten of the messages (20,000 of all kinds) he receives daily. During the presidential election campaign, Ms von Baer answered every message to @enavonbaer herself, but now her staff respond, or pass questions on to other ministries.

Twitter works well for extrovert and conscientious individual politicians. Denis Coderre (@deniscoderre) started using it for relief and rescue messages after the Haitian earthquake in January (his electoral district in Montreal has a big Haitian population). He writes social messages, such as commentaries on ice-hockey matches (he was a sportscaster before he became a politician). A second category is service messages for his constituents. A third is purely political. To benefit, a politician must do all of them himself, he says. But few match his talent or output. Twitter may feel personal but it is all too public. The risk is asymmetric. An ill-judged tweet can do severe, instant damage. Kerry McCarthy, a Labour candidate in Britain's election, revealed early postal-vote counts in a tweet that ended “#gameON!”. That may have seriously breached electoral law.

As well as boosting the profile of individual politicians, Twitter may be better designed for campaigning and opposition than for governing. “We'll change Washington” is easy to fit into 140 characters. Explaining the messy and inevitable compromises of power is a lot harder. In January of this year a study by Fleishman Hillard, a Washington PR firm, discovered that Republicans in the House twittered more than five times as often as Democrats. Ms von Baer says that the Chilean opposition uses Twitter to make up for its poor coverage in the mainstream media.

Not really real life

The days when tweets involved a sweaty-thumbed real-life politician giving candid thoughts on the day's events may be passing. Risk-averse politicians are likely to make their tweets bland, and bland tweeters may be less likely to be followed. Once politicians understand that everything is public, they are much less likely to offer the unadorned truth, at least to ordinary voters. William Hague, a top Tory politician, amused his followers by responding to a tweeted inquiry about the menu at a recent fast-food supper (Chicken Royale and a Fanta)—but his interrogator was not just anyone, but Bryony Gordon, a hotshot columnist for a national daily. Few subjects will ever come truly close to their sovereigns. But the impression of doing so remains tantalising.