2,000 yards. It is, however, desirable that a few pieces of greater power should also be mounted on the batteries. I therefore consider that a few of the latest type of 8-inch breech-loading guns shall form part of the armament. These will pierce 7 inches of iron at 3,000 yards. The question of the power of gun required in the defensive batteries of course depends upon the description of vessels by which these colonies may be attacked. All authorities agree that ships of war, of some sort, may make a descent upon Australasia, but a difference of opinion sometimes arises as to whether a hostile iron-clad is likely to appear in these waters. Though I believe that the class of vessel by which we are most likely to be attacked is a swift ship, of great coal-carrying power, such as I will hereafter describe, it appears to me that, in determining on our plans, it would be unwise to act on the assumption that vessels protected by iron-plates, in greater or less degree, may not be employed in the attack. As regards the designs of the works for the reception of the guns already in the colony, as the carriages and platforms supplied for them are arranged for batteries “en barbette” (see Plate IV.), i.e., guns with a wide sweep firing over a parapet, that system will, as a rule, be adopted. The only exception to this will be in a case, to which I shall hereafter refer, where it will be necessary to place the guns in casemates in order to protect them from fire from heights in their rear. Designs for batteries. With respect to the guns not yet provided, it is proposed that they shall be mounted on “disappearing” carriages by means of which—excepting at the time of actual firing, when the gun and one man only is exposed—both gun and gunners are absolutely protected from an enemy's fire. I pass on to consider the use of submarine mines, which should, when practicable, be employed in the defence of harbours, in order to stop an enemy's ships and detain them under the fire of the batteries. I am glad to find that Admiral Scott, of Dunedin, so well known at the Admiralty for the great improvements which he effected in regard to ships' gun-carriages, is specially advocating the adoption of this element of defence. Submarine mines. Twenty years ago there was very little method in employing these engines of war, but now the application of them has become quite a complicated science. They may be divided into three classes, viz., mechanical mines, observation mines, and electro-contact mines.