Last night the transports were merely taking up their positions, and the real exit of the armada from Mudros commenced this afternoon at about 2 o'clock. The weather, which was threatening at an early hour, has now become perfectly calm, and if it only lasts the conditions will be ideal for a rapid disembarkation. Throughout the morning transports steamed out to take up their respective positions in the open sea. The same enthusiastic scenes were witnessed as yesterday. The covering forces will be put ashore from certain battleships, while others will sweep the enemy's positions with their guns and endeavor to prevent them from shelling the troops while disembarking. It is generally considered that the critical period of the operations will be the first twenty-four hours, and the success or failure of the whole enterprise will depend on whether these covering parties are able to obtain a firm foothold and seize the positions which have been assigned to them. Every detail has been worked out and rehearsed, and every officer and man should now know the peculiar role which has been assigned to him. The navy will have entire charge of the landing of these thousands of men. Beach parties will go ashore with the first of the troops, and officers from the ships will direct the movements of all the boats as they bring the troops ashore. This battleship belongs to a division which will consist of the Australians, who are to land near Gaba Tepe. We are one of the landing ships, and this afternoon received on board 500 officers and men of the Australian contingent who are to form part of the covering force. They are a magnificent body of men, and full of enthusiasm for the honorable and dangerous role given to them. At 2 o'clock the flagship of this division took up her position at the head of the line. We passed down through the long line of slowly moving transports amid tremendous cheering, and were played out of the bay by the French warships. No sight could have been finer than this spectacle of long lines of warships and transports, each making for its special rendezvous without any delay or confusion. At 4 o'clock this afternoon the ship's company and the troops were assembled on the quarterdeck to hear the Captain read out Admiral de Robeck's proclamation to the combined forces. This was followed by a last service before battle, in which the chaplain uttered a prayer for victory and called for the Divine blessing on the expedition, while the whole of the ship's company and troops on board stood with uncovered and bowed heads. We are steaming slowly through this momentous night toward the coast and are due at our rendezvous at 3 A.M. tomorrow, (Sunday,) a day which has so often brought victory to the British flag. THE SECOND DISPATCH. Dardanelles, April 25.