But, once Lord Aberdeen was installed in Downing Street, M. Guizot's objections to proceeding with the slave trade convention disappeared. The necessary powers were sent to Sainte-Aulaire, the French ambassador, and, on December 20, 1841, the treaty, regulating the right of search, was signed in London. It was soon clear, however, that M. Guizot had been mistaken in supposing that the Chamber would agree to ratify the agreement into which he had entered. The opposition to slavery had never been so pronounced in France as in England, and the Treaty of July had greatly stimulated the old feeling of jealousy of British maritime supremacy. By reason of England's naval preponderance, the duty of stopping suspected vessels must necessarily devolve chiefly upon her officers. Both in the French Chambers and in the press it was hotly contended that the new treaty was but a device, by means of which England purposed to arrogate to herself the right of policing the sea. So keen was this feeling that M. Guizot was forced to inform the British government that France would be unable to ratify. Popular opposition, it was thought, would diminish with time, and the protocol was accordingly kept open, in the hope that France might still become a party to the treaty. But this expectation was not fulfilled, and on November 9, 1842, the definite withdrawal of France was officially communicated to Lord Aberdeen. The affair caused no little resentment and disappointment in England. Three years later, however, M. Guizot was enabled to re-open the question. By that time the relations of the two countries were upon a more friendly footing, and the Duc de Broglie and Dr. Lushington, the commissioners of their respective governments, succeeded, in consequence, in arriving at an agreement. The new treaty, signed on May 29, 1845, fulfilled all the essential conditions of previous conventions, but provided that, in future, the right of search in African waters should be exercised by a joint Franco-British squadron.[716] Spanish affairs, however, were destined to be the question which was to occupy the chief attention of the two governments. It has been related how, in the autumn of 1840, Christina had been forced to quit Spain, and how, in the spring of the following year, the Cortes had elected Espartero sole Regent of the kingdom. This solution of the difficulty was by no means acquiesced in as satisfactory by all parties. The elevation of the popular general to the head of the government was necessarily regarded as a victory for the _Progressistas_ and, consequently, as a triumph for English diplomacy. Indeed, since the abdication of the Queen-Mother, the _Moderados_, as a parliamentary party, had almost ceased to exist. But their leaders still continued to correspond with Christina, whose house in the Rue de Courcelles in Paris soon became the centre of a vast conspiracy against the new Regent.