on building houses and hydraulic works, on mining, on the chase, and forestry, they are all confined within very limited spaces which may be soon explored with sufficient exactness. But the Commander in War must commit the business he has in hand to a corresponding space which his eye cannot survey, which the keenest zeal cannot always explore, and with which, owing to the constant changes taking place, he can also seldom become properly acquainted. Certainly the enemy generally is in the same situation; still, in the first place, the difficulty, although common to both, is not the less a difficulty, and he who by talent and practice overcomes it will have a great advantage on his side; secondly, this equality of the difficulty on both sides is merely an abstract supposition which is rarely realised in the particular case, as one of the two opponents (the defensive) usually knows much more of the locality than his adversary.
This very peculiar difficulty must be overcome by a natural mental gift of a special kind which is known by the—too restricted—term of Ortsinn sense of locality. It is the power of quickly forming a correct geometrical idea of any portion of country, and consequently of being able to find one’s place in it exactly at any time. This is plainly an act of the imagination. The perception no doubt is formed partly by means of the physical eye, partly