The other bad feature about the preparations was the arrangement for dipping the respirators in solution in the trenches, as referred to above. During the attack a lot of the men dipped their respirators in water; which of course washed the chemicals out of the respirators and made them ineffectual much sooner than they should have been. But all of these matters were remedied before another gas attack was made. After the first emergency respirator had been issued every effort was made to devise a more effective form of protection than that given by the cotton-wool pads, in expectation of a recurrence of German attacks. As a matter of fact there were no attacks between the beginning of June and December, 1915, because the wind was unfavourable to the Germans. This was another point that they had apparently overlooked, because on investigation we found that the prevailing winds in Flanders blew from west to east, and that about three-quarters of the total winds were in our favour and against the Germans. The long interval of the summer of 1915 gave us a splendid opportunity to develop the protection against gas which had been commenced in the spring while attacks were still being made. The most important of these developments were the invention of the celebrated “smoke helmet” and the use of sprayers for the removing of gas from the trenches. We also found out the exact value of certain other devices and methods which had been suggested for combating the gas clouds, and a lot of impossible ideas were consequently turned down. The latter might be discussed first of all. One suggestion which was made and believed in by most people at various times--including the Germans themselves--was that fires built in the trenches or on the parapet would cause such an upward draft as to lift up the gas cloud and carry it safely over our heads. Experiments showed, however, that this idea was absolutely false, because though an upward draft was certainly formed the incoming air carried with it just as much gas from the surrounding atmosphere, and nothing was gained by it. It was a long time before the Germans tumbled to this, and even many months later their own instructions on defence against gas included statements that showed their reliance on this procedure. One suggestion which actually reached the point of being acted on was that the gas cloud could be dispersed by an explosion, and for this purpose we were provided with wooden boxes filled with black powder and with fuses attached, which we were supposed to light at the crucial moment and throw into an advancing cloud. This heroic procedure was never actually made use of, however, because experiments in the meantime again showed that such explosions had very little effect on a cloud of gas. Two suggestions which really did turn out to be winners were those referred to previously--the smoke helmet and the Vermorel sprayer for clearing the trenches.