On the same day, July 30, M. Cambon reminded Sir Edward Grey of a letter written by the latter on November 22, 1912, agreeing that while consultations between military and naval experts of their two nations did not pledge their Governments to co-operate, yet, should either Government have grave reason to expect an unprovoked attack by a third Power, or something that threatened the general peace, it should immediately discuss with the other whether, and by what measures, they should co-operate in opposition. M. Cambon also showed a letter from the French Foreign Minister, indicating that Germany was preparing to invade France. Sir E. Grey answered next day, after a Cabinet Council, that as yet Great Britain could not definitely pledge herself to intervene. The preservation of the neutrality of Belgium might be an important factor in determining the British attitude. Sir E, Grey also asked the French and German Governments, through their Ambassadors, whether they were prepared to respect Belgian neutrality provided it was not violated; and he asked the Belgian Government whether it would remain neutral. France and Belgium replied affirmatively at once. The German Government temporised, and eventually gave no answer, though Sir Edward Grey had warned the German Ambassador on August 1 of the probable effect of a violation on public feeling in Great Britain. Meanwhile Russia and Austria were still negotiating (July 30, 31). On the 29th Germany had suggested to Austria that she should content herself with occupying Belgrade. That night Russia offered to stop all military preparations if Austria would recognise that the Austro-Serbian conflict had become a matter of general European interest, and would eliminate from the ultimatum the points involving a violation of the sovereignty of Serbia. Austria now agreed at last to discuss the whole question of her ultimatum, and Russia asked the British Government to assume the direction of these discussions. But the hope of peace thus held out was wrecked by the German ultimatum requiring Russia to countermand her mobilisation. Germany, meanwhile, had gone further towards mobilisation than Russia; the German Secretary of State refused to discuss a last proposal from Sir Edward Grey for joint action of Great Britain, Germany, France, and Italy, pending a reply from Russia; and on the afternoon of August 1 Germany declared war against France. Next morning the Germans violated the neutrality of Luxemburg. British merchant ships had already been detained at Hamburg--though the detention was temporarily countermanded on representations from the British Ambassador--and the only question now left for the British Government was whether Great Britain should remain neutral. The determining factors proved to be the violation of Belgian neutrality and the danger to France; and the position was fully explained by the Foreign Secretary on August 3 (p. 170) and by the Prime Minister two days later.