Though the Germans began their use of gas by releasing it from cylinders, depending upon the wind to carry it over the enemy’s lines, these “cloud attacks,” as they were called, did not prove satisfactory and were eventually discontinued, for great difficulty was experienced in getting the heavy cylinders up to the front and installing them in the trenches, and favorable winds could not be depended upon. It seems likely, indeed, that the Germans failed to recognize the significance of the meteorological records and charts of northern France, which show that 75 per cent of the prevailing winds are from a southerly or southeasterly direction, thus leaving the Germans only 25 per cent of the time in which they could use their gas without danger of its being blown back over their own lines. It was in order to overcome these meteorological conditions that the Germans evolved the idea of loading the gas into shell, usually in the form of liquid, which turned into gas when it came into contact with the air upon the explosion of the shell, and firing these shell from guns or mortars, thus enabling them to place the gas wherever they desired without reference to the weather. During the last two years of the war, barring a few isolated instances, gas was used in no other way. The filling of shell was, therefore, one of the most important of Edgewood’s many activities. Let me explain to you, as simply and briefly as possible, how the shell were filled with phosgene. The empty shell, after inspection, were loaded on trucks together with the required number of loaded boosters. (A booster, it should be explained, is the cap or stopper containing a charge of high explosive, usually TNT or dynamite, which is screwed on the nose of the shell after it has been filled with gas, much as a metal top is screwed onto a bottle. Just before firing, a fuse is inserted in the booster, igniting the explosive, which in turn shatters the shell, thus releasing the gas.) The trucks with the empty shell were then run by electric locomotives to the filling buildings. Here the shell were transferred to a conveyer, a sort of moving platform, which slowly moved through a room kept cold by refrigeration. About thirty minutes was required for this operation, during which time the shell were cooled to a temperature of about zero. This chilling of the shell was made necessary because phosgene has a low boiling-point. It was imperative, therefore, that the temperature of the shell be kept considerably below the boiling-point of phosgene in order that the latter should remain in liquid form while the filling was taking place. The chilled shell were then transferred to trucks and hauled by motor through the filling-tunnel to the filling-machines. Here the phosgene, kept in liquid state by refrigeration, was run into the shell by automatic machines. The truck then carried the filled shell forward a few feet, at which point the boosters were screwed into the noses of the shell by hand.