The assurances and explanations of Count Nesselrode were accepted as satisfactory by Lord Palmerston. The visit of the Tsarewitch, the future Alexander II., to London, in the spring of 1839, contributed still further to restore harmonious relations. Nevertheless, the general situation which confronted Palmerston was disquieting. Russia, which by means of the Treaty of Unkiar-Skelessi had assumed the exclusive protectorship of Turkey, now appeared to exercise a dangerous ascendency over the Court of Persia. Although the Shah had been compelled to raise the siege of Herat, and although the proceedings of Simonitch and Witkewitch had been disavowed, there was room for grave anxiety. Distant as was the frontier line of the Sutlej from the most advanced Cossack posts, the presence of Russian agents in the intervening States foreboded trouble. At Lahore, Hyderabad and Cabul, the appearance of a new power in Central Asia could not fail to be eagerly discussed. But it was not alone the advance of Russia beyond the Caspian which gave those responsible for the safety of British India cause for uneasy reflection. At this time, when the introduction of steam as a means of transport was making the question of rapid communication a matter of the first importance, Mehemet Ali was building up an Arab Empire which already extended from Khartum to the Taurus mountains and the Persian Gulf. Whether in the future the Indian mail would be carried over the Isthmus of Suez, or whether Colonel Chesney should succeed in establishing steam communication by way of the Euphrates, the ruler of Egypt was master of either route. Nor did he stand alone. Whilst busily engaged in strengthening her own position as a Mediterranean power, England's most formidable naval rival was showing a marked disposition to befriend him. In Syria France was the acknowledged protector of the Catholics, and her influence was reported to have increased of late years.[471] From Algiers she was extending her grasp over the whole north coast of Africa, whilst in Spain she was striving to re-establish that predominating influence which she had formerly exercised. It seemed possible that France, in alliance with Spain and Mehemet Ali, might yet be enabled to realize Napoleon's dream of converting the Mediterranean into a "French lake."