this sort of piston action, repeated on a big scale by the constant passage of trains bound in opposite directions in the two tunnels, was supposed to keep air moving along each of the tunnels and between them through the cross-passages in such a way as to allow for its steady replenishment through the length of the tunnels. With modifications, Low's concept of a double self-ventilating tunnel forms the basis for the plan most seriously advanced by the Channel Tunnel Study Group in 1960. After showing his plans to Thomé de Gamond, who approved of them, Low obtained the collaboration of two other Victorian engineers—Sir John Hawkshaw, who in 1865 and 1866 had had a number of test borings made by a geologist named Hartsink Day in the bed of the Channel in the areas between St. Margaret's Bay, just east of Dover, and Sangatte, just north-east of Calais, and had become convinced that a Channel tunnel was a practical possibility in geological terms; and Sir James Brunlees, an engineer who had helped build the Suez Canal. In 1867, an Anglo-French committee of Channel-tunnel promoters submitted a scheme for a Channel tunnel based on Low's plan to a commission of engineers under Napoleon III, and the promoters asked for an official concession to build the tunnel. The members of the commission were unanimous in regarding the scheme as a workable one, although they balked at an accompanying request of the promoters that the British and French Governments each guarantee interest on a million sterling, which would be raised privately, to help get the project under way, and took no action. But apart from the question of money the promoters were encouraged. In 1870 they persuaded the French Government officially to ask the British Government what support it would be willing to give to the proposed construction of a Channel railway tunnel. Consideration of the question in Whitehall got sidetracked for a while by the outbreak of the Franco-Prussian war in the same year, but in 1872, after further diplomatic enquiries by the French Government, the British Government eventually replied that it found no objection "in principle" to a Channel tunnel, provided it was not asked to put up money or guarantee of any kind in connection with it and provided that ownership of the tunnel would not be a perpetual private monopoly. In the same year, a Channel Tunnel Company was chartered in England, with Lord Richard Grosvenor, chairman of the London, Chatham & Dover Railway, at its head, and with Hawkshaw, Low, and Brunlees as its engineers. The tunnel envisioned by the company would stretch from Dover to Sangatte, and its cost, including thirty-three miles of railway that would connect on the English side with the London, Chatham & Dover and the South-Eastern Railways, and on the French side with the Chemin de Fer du Nord, would be £10,000,000. Three years later, the English company sought and obtained from Parliament temporary powers to buy up private land at St.