Remaining calm must have required extraordinary self-control. Internment had just been introduced and the British army had entered Derry's nationalist Bogside in strength. Violence looked inevitable, as residents poured on to the streets. Hume's response was to ask the demonstrators to sit down and to negotiate with the local army commander, who agreed to withdraw his troops. But a second regiment and its commander refused to move and turned water cannon on the crowd.
Hume describes, in his new book published today, what happened next. "I got up and walked towards them with my hands up, and they repeatedly knocked me down with the jet from the hose. Finally, some soldiers grabbed me and put me up against a wall, where they photographed me, and then arrested me, charging me with obstructed Her Majesty's forces."
After all that many might have fallen in with the "men of violence", given that the avenues for sane negotiation had been so determinedly closed. But Hume's reaction was typically stubborn. He refused to pay a pounds 20 fine and took his case to the House of Lords. There, he eventually proved that the British army's action in Northern Ireland that day had been illegal, because it had not been sanctioned by Parliament. Indirectly, the incident and its aftermath led, in March 1972, to the imposition of direct rule of Northern Ireland from London. In apparent defeat, Hume found a route to victory.
Such success has long vindicated his lifelong opposition to violence. But keeping one's temper isn't easy, especially for someone with years of injustice and political tension burning in his heart. But his repression and refashioning of anger into political action, have made him what he is: one of the most creative and imaginative constitutional nationalists in Irish history.
In achievement, he stands beside two figures, who likewise eschewed violence: Daniel O'Connell and Charles Stewart Parnell. In their time, they, too, were visionaries, recognising that, despite its apparent weaknesses, peaceful nationalism enjoyed considerable room for manoeuvre. Thus, in the 1820s. O'Connell forged a lasting alliance between Catholicism and nationalism, around the issue of Catholic Emancipation. In the 1880s, Parnell, a Protestant, created Britain's first modern, disciplined political party, a powerful bloc of Irish MPs, who held the balance of power at Westminster and pushed the Prime Minister, William Gladstone, into backing Home Rule for Ireland.
Hume's great insight was to recognise early on that Britain had, in the main, lost interest in Northern Ireland, save for wishing to maintain peace and stability. He has sought to convince London that peaceful nationalists such as himself, rather than a Unionism that is bankrupt of fresh thinking, can create that stability.
To that end, and to strengthen his minority community, he has forged alliances, with the Americans, Dublin and in Europe, convincing all that peaceful, moderate nationalism is the way forward. In securing the IRA's ceasefire in August 1994, Hume seemed also to have convinced even the modern exponents of "physical force" nationalism that his way, the constitutional route, the talking method, offered greatest hope for success. The all- party talks on Northern Ireland, which begin today, owe a great deal to Hume's analysis and lobbying.
But if there is a crucial weakness in Hume as a visionary, it may be the same failing thatafflicted O'Connell and Parnell - an inability to win over Protestants in substantial numbers.
Hume, like his predecessors, is not sectarian; his party proudly boasts that Protestants occupy senior positions. And he, himself, has insight into what motivates Unionists. He says that their uncompromising behaviour "can only be understood, if they are seen, as they feel themselves to be, as a threatened minority on the island of Ireland". He reassures them, explains that they have nothing to fear, that the constitutional link with Britain will remain, while a majority in Northern Ireland desires it. In Derry, where Hume's party, the SDLP, controls the council, nationalism is gracious: every other year a Unionist is appointed mayor.
Yet, for all his understanding, Hume still seems not to hold the all- important key to Unionist hearts. You can see why, by reading his book. It sets clear limits on the methods that nationalism is entitled to use: they must be peaceful.
But Hume sets no limits on the aspirations of nationalism. The goal remains a united Ireland, albeit achieved by persuasion and without coercion.
In his mind, Europe is the model for a future Ireland. If the European Union, forged out of conflict that left 35 million dead in two world wars, can be peaceful, then why can't his people make a new Ireland that buries the old animosities? Hume, an MEP and one of the first Euro-enthusiasts, believes that, as with the EU, it is possible through years of discussion and co-operation to achieve closer and closer Irish union.
A few years ago, this argument seemed sound. But Europe is no longer an acceptable template. The reservations of Euro-sceptics have forced enthusiasts for Europe to abandon talk about some golden, but incohate Euro-future (which the sceptics see as conscious or unconscious code for federalism) and make explicit the limits of what they seek.
The same goes for nationalists. Unionists are unlikely to budge from their state of defensiveness and intransigence as long as nationalism sets no limits on its agenda. Hume's brilliance has been to nurture and exploit the power of constitutional nationalism, so creating hope for Catholics in Northern Ireland and discrediting the use of violence.
The big question is whether he will, in the end, stand above O'Connell and Parnell and become the nationalist who finally won over the Unionists by promising: "We want to go this far and no further."
`John Hume: personal views, politics, peace and reconciliation in Ireland' is published by Airlift Book Company.