bridges, woods, and rivers, and when the column has arrived in the presence of the enemy, and the conduct of flank marches, marches in retreat, and the simultaneous movement of several columns.  The importance of precautions against surprise, of preserving the mobility of the columns, and of providing for concentration on short notice whenever it may be necessary, is not lost sight of, but is dwelt upon with great frequency.  But military rules are not more inflexible than other human rules.  Though they are based upon fixed principles, cases may, and do, arise when they cannot be strictly adhered to,—­sometimes when they ought not to be.  When should they be strictly observed?  When and how far is it prudent to depart from them?  “These questions,” says General Dufour, “admit of no answers.  Circumstances, which are always different, must decide in each particular case that arises.  Here is the place for a general to show his ability.  The military art would not be so difficult in practice, and those who have become so distinguished in it would not have acquired their renown, had it been a thing of invariable rules.  To be really a great general, a man must have great tact and discernment in order to adopt the best plan in each case as it presents itself; he must have a ready coup d’oeil, so as to do the right thing at the right time and place; for what is excellent one day may be very injurious the next.  The plans of a great captain seem like inspirations, so rapid are the operations of the mind from which they proceed:  notwithstanding this, everything is taken into account and weighed; each circumstance is appreciated and properly estimated; objects which escape entirely the observation of ordinary minds may to him seem so important as to become the principal means of inducing him to pursue a particular course.  As a necessary consequence, a deliberative council is a poor director of the operations of a campaign.  As another consequence, no mere theorizer can be a great general.”

Battles, on which the fortune of the campaign must turn at last, receive a large share of attention.  The decision of the question as to when they shall be fought, though sometimes admitting of no choice, is more often, with a skilful general, a matter of pure calculation, depending upon fixed principles, which General Dufour recites in a few brief, but suggestive sentences.  His directions for the disposition and manoeuvres of the forces in both offensive and defensive battles are quite complete, though the thousand varying circumstances by which these may be modified, and which render it impossible for one battle to be a copy of another, can only be hinted at.  Among the elements of a battle here considered are the disposition of the forces, the manner of bringing on and conducting the engagement, the manoeuvres to change position on the field, bringing on reinforcements, seizing all advantages that may offer, and the manner of conducting pursuit or retreat.  The attack and defence of