peat what
has already been said, no matter what may be the relative cost of ships
and forts, the one, as a general thing, cannot be substituted for the
other. Each has its own sphere of action, and each will contribute, in
its own way, to the national defence; and any undue increase of one, at
the expense of the other, will be attended by a corresponding diminution
of national power.[25]

[Footnote 25: For further information concerning our system of sea-coast
defences, the reader is referred to House Doc. 206, twenty-sixth
Congress, second session; Senate Doc. 85, twenty-eighth Congress, second
session; and to the annual reports of the Chief Engineer.]

CHAPTER VIII.

OUR NORTHERN FRONTIER DEFENCES.

In discussing engineering as a branch of the military art, we spoke of
the use of fortifications on land frontiers, and their influence on the
strategic operations of a campaign. A brief notice was also given of the
different systems that have been proposed for arranging these defensive
works. Let us now apply this discussion to our northern frontier.

The principle laid down by Napoleon and Jomini, "that fortifications
should always be constructed on important strategic points," is
undoubtedly the correct one: but how to determine these points is a
question that will often perplex the patience and try the skill of the
engineer; yet determine them he must, or his fortifications will be
worse than useless; for a fort improperly located, like a cannon with
its fire reversed on its own artillerists, will be sure to effect the
destruction of the very forces it was designed to protect.

The selection of positions for fortifications on our northern frontier
must have reference to three distinct classes of objects, viz.: the
security, _first_, of the large frontier towns, where much public and
private property is exposed to sudden dashing expeditions of the foe,
made either on land or by water; _second_, of lake harbors, important as
places of refuge and security to our own ships, or to the enemy's fleets
while engaged in landing troops or furnishing supplies to an invading
army; _third_, of all strategic points on the probable lines of
offensive or defensive operations. These objects are distinct in their
nature, and would seem to require separate and distinct means for their
accomplishment; nevertheless, it will generally be found that positions
selected with reference to one of these objects equally fulfil the
o