In deciding the strength of a column for an expedition against the North West Frontier tribesmen, the first requisite, having regard to the foregoing considerations, is so to limit numbers, that, in the topographical conditions likely to be met, the force can, as an entirety, make a march of reasonable length, let us say eight or ten miles. Assuming that the column will move at an average rate of about two miles per hour, that, in order to avoid risk of disaster, it is, as a rule, desirable for the main force not to march before dawn, and to be in camp by dusk, and that ten--twelve hours of daylight are available, it is clear that the road space occupied must not, for a ten mile march, exceed ten to fourteen miles. That is to say, the numbers that can fulfil this condition on a narrow track, amount to about 4500 fighting men, carrying three days' rations on the person, and five days' on transport animals. Suppose that four such columns are destined to invade the Afridi Tirah. The Afridis are said to possess 25,000 to 30,000 fighting men, and if it be assumed that two-thirds of these have breech loading rifles, and that the whole mass is unlikely to attack any, one, or even two columns, the largest hostile gathering that a British detachment may expect to meet is 6000-8000 men, of whom 4500-5500 may be well armed. A column of 4500 disciplined troops need not therefore fear reverse. The composition of a column is regulated by the topography of the area of operations, but the following example will show how the allotment of troops may be determined. As basis for calculation a mixed brigade[1] organised for independent action may be taken. To these troops may be added a squadron of Silladar cavalry, if the country is suitable to its action, and a mountain battery, which, together with the infantry, form a handy force of the three arms. But the column is still weak in infantry, on which the brunt of the fighting will necessarily fall, and possesses no technical troops for road-making, etc. Both requirements may be fulfilled by the addition of a pioneer battalion, or, since some hold that sappers and miners are more economical than pioneers, a battalion, of British infantry, or of Gurkhas, and a company of sappers and miners may be included. It now only remains to give the troops an ammunition column, the necessary staff, certain additional medical, and administrative details, and the force--one infantry brigade organised for independent action, one squadron, one mountain battery, one British battalion, one company sappers and miners, etc.--will be complete, and adequate for its purpose. FOOTNOTES: [Footnote 1: 1 British infantry battalion; 3 Native infantry battalions; 1/2 British field hospital; 1-1/2 Native field hospitals; 1 Field post office; Brigade supply column.] MARCHES AND PROTECTION.