The location of these Headquarters on our side of the line is a constant object of solicitude to the enemy on the other. Very few officers even on our side know where they all are. I had confided to me, for the purpose of my official duties, a complete list of such Headquarters, and the first thing I did, in pursuance of my instructions, was to commit it to memory and then burn it. To find out the enemy's H.Q.--with a view to making them as unhealthy as possible--is almost entirely the work of aeroplane reconnaissance. To discover the number and composition of the units whose H.Q. they are is the work of our "Intelligence." Of our Intelligence work the less said the better--by which I intend no aspersion but quite the contrary. The work is extraordinarily effective, but half its effectiveness lies in its secrecy. It is all done by an elaborate process of induction. I should hesitate to say that the "I" officers discover the location of the H.Q. of captured Germans by a geological analysis of the mud on the soles of their boots, in the classical manner of Sherlock Holmes; but I should be equally indisposed to deny it. There is nothing too trivial or insignificant to engage the detective faculties of an "I" man. He has to allow a wide margin for the probability of error in his calculations; shoulder-straps, for example, are no longer conclusive data as to the composition of the enemy's units, for the intelligent Hun has taken of late to forging shoulder-straps with the same facility as he forges diplomatic documents. Oral examination of prisoners has to be used with caution. But there are other resources of which I shall say nothing. It is not too much to say, however, that we have now a pretty complete comprehension of the strength, composition, and location of most German brigades on the Western front. Possibly the Germans have of ours. One thing is certain. Any one who has seen the way in which an Intelligence staff builds up its data will not be inclined to criticise our military authorities for what may seem to an untutored mind a mere affectation of mystery about small things. In war it is never safe to say _De minimis non curatur_.