The deadly and effective method of directing artillery fire on hostile batteries by means of wireless telegraphy played a great part in winning the war, but for the first battle of Ypres the wireless machines were not ready in quantity. The penalty which had to be paid for this unreadiness was heavy. Precious shells, which were all too few, had to be expended for ranging purposes. On the 4th of November Lord Kitchener wired to Sir John French: 'I have been talking to David Henderson about giving more observation to artillery by aeroplanes. As this saves the ranging ammunition, which is worth anything to us, please insist upon it.' Failing wireless, other methods of ranging had to be employed. These methods had been set forth in an official paper issued on the 28th of October. The aeroplane flies at any convenient height and when it is exactly above the target it fires a Very light. The battery range-finders, who have been following its course, then take its range and another observer with the battery takes its angle of elevation. These two observations are sufficient to determine the horizontal distance between the battery and the target. It was sometimes found difficult to take the range of an aeroplane, at a given moment, with an ordinary range-finder, and an alternative method of ranging is suggested. By this method the aeroplane flies at a prearranged height, and, as before, fires a light exactly over the target. But this method also is liable to error, for an aeroplane determines its height by the use of a barometer, and barometers are only approximately accurate for this purpose. So it was suggested that the two methods should be combined: the aeroplane should endeavour to fly at a fixed height, and the range-finders should, if possible, also make their calculations. These methods cannot attain to the accuracy of wireless, but they were found in practice to give fairly good results. They were not quickly or generally adopted; many battery commanders continued to prefer the reports of their trained ground observers to the indications given from the air. When wireless machines were increased in number, artillery observation from the air came into its own. In a report dated the 5th of February 1915, Brigadier-General Stokes, commander of the 27th Divisional Artillery, lays stress on the enormous advantages of wireless. He says that the 116th Heavy Battery of the Royal Garrison Artillery, which had at its disposal an aeroplane equipped with a lamp, had succeeded in registering only three targets in fifteen days, whereas the 130th Howitzer Battery, which had a share in the services of a wireless aeroplane, had registered eight targets in seven days. The disadvantages of the older and cruder method are many; a thin mist which does not prevent the aeroplane from observing the target is enough to prevent signalling to the battery; the lamp is difficult to use on a rough day, and difficult to read against the sun; the aeroplane has to