One thing that the Germans had not counted upon was the fact that the prevailing winds in Flanders blow from west to east. During the entire summer and autumn of 1915, the winds refused to favor them, and no gas attacks were staged from June to December. This gave the British a long respite and enabled them not only to prepare better gas-masks, but also to make plans to give the Hun a dose of his own medicine. [Illustration: (C) Kadel & Herbert Liquid Fire Streaming from Fixed Flame-throwing Apparatus] WHEN THE WIND PLAYED A TRICK ON THE GERMANS There were many disadvantages in the use of gas clouds, which developed as the Germans gathered experience. The gas started from their own lines in a very dense cloud, but the cloud grew thinner and thinner as it traveled toward the enemy, and lost a great deal of its strength. If the wind were higher than fifteen miles an hour, it would swirl the gas around and dissipate it before it did much harm to the opposing fighters. If the wind were light, there were other dangers. On one occasion in 1916 a cloud of gas was released upon an Irish regiment. The wind was rather fickle. It carried the gas toward the British trenches, but before reaching them the cloud hesitated, the wind veered around, and soon the gas began to pour back upon the German lines. The Germans were entirely unprepared for this boomerang attack. Many of the Huns had no gas-masks on, and those who had, found that the masks were not in proper working-order. As a result of this whim of the winds, eleven thousand Germans were killed. [Illustration: Courtesy of "Scientific American" Cleaning Up a Dugout with the "Fire Broom"] While chlorine was the first gas used, it was evident that it was not the only one that could be employed. British chemists had suspected that the Germans would use phosgene, which was a much more deadly gas, and in the long interval between June and December, 1915, masks were constructed which would keep out not only the fumes of chlorine but also the more poisonous phosgene. In one of their sorties the British succeeded in capturing some valuable notes on gas attacks, belonging to a German general, which showed that the Germans were actually preparing to use phosgene. This deadly gas is more insidious in its action than chlorine. The man who inhales phosgene may not know that he is gassed. He may experience no ill effects, but hours afterward, particularly if he has exercised in the meantime, he may suddenly fall dead, owing to its paralyzing action on the heart. FREEING THE BRITISH TRENCHES OF RATS