Source: First Hints On Rifle Shooting by A.P. Humphry (William Clowes and Sons, London, 1876)
It is well to begin at once to contract the habit of noticing the direction and strength of the wind, and the indications of them afforded by flags, the smoke from rifles, the rustling of leaves, and other signs. The firer should be on the alert as to these the whole time he is on the range, and experience will teach more about the effect of wind upon the bullet, and the way to judge it, than all the books that could be written. At 600 yards the very gentlest perceptible wind will deflect the Snider bullet one or two feet, and in a gale it may be necessary to aim perhaps 18 feet off the target. The allowance required at 600 yards is quite half as much again as at 500 for the same wind. A wind blowing from the rear aids the bullet in its course, and tends to throw it over the target, while a head wind exercises a retarding, and hence depressing, influence.
As long as the wind remains steady there is no great difficulty in dealing with it, inasmuch as, after the allowance is once ascertained, nothing but steady shooting is required; but, when the wind so constantly changes its force and direction, that a fresh calculation has to be made before firing every shot, then it is that the skill of the rifleman is tested to the utmost, and he must give his whole mind to watching every change, and, if possible, its effects upon the shots of other firers. This watching of the results of other men, though often a source of much assistance, nevertheless requires the greatest discretion; in each case, unless the firer be a known and steady shot, his results are not worth taking into account, because it is impossible to tell how far the causes chiefly affecting them are external to himself. Indeed, in no case is it wise blindly to adapt one's judgment to the results obtained by other firers; such results should only be taken as means of calling the attention to conditions of the wind, which might otherwise have escaped notice, and no change of aim should be made unless the actual reason for it is clearly made out. If the advisability of a change is doubtful, it is better not to make it. During the aim the attention must be sufficiently on the alert against a change of wind, which may at the last moment upset all the most careful calculations. Of course, with all precautions, a misfortune of this kind will sometimes surprise us at the moment of firing; nevertheless, much may be done to prevent it by not taking a longer aim than is absolutely needed, and by firing each shot, as far as possible, at a moment when the wind seems likely to hold firm.
Perhaps the most disappointing days for shooting are those on which the wind has not sufficient strength to lift the flags, but the atmosphere seems nevertheless lazily to swing to and fro. Before the firing, the apparent absence of wind gives every hope of brilliant shooting, but the uncertain manner in which the bullets strike first one side of the target and then the other, and the extreme difficulty of judging the right aim to be taken for each shot, soon induce a feeling of contentment with a very moderate performance.
Some ranges, from the conformation of the ground, or the proximity of trees or buildings, are subject to peculiar currents of wind. These are of course soon learnt by the habitué, but such experience is of little use for firing in other places. Undoubtedly it is a great advantage to have learnt to shoot upon a range situated in an open country, where the path of the bullet is neither unduly sheltered from the wind, nor exposed to any local diversion of its force. Knowledge acquired on such a range is useful everywhere, but a person whose practice has been confined to a range of the former sort can only possess a very distorted knowledge of the true effects of wind.