It was at this period that, according to Mr. Coxwell, Lord Wolseley made ascents at home in a war balloon to form his own personal opinion of their capabilities, and, expressing this opinion to one of his staff, said that had he been able to employ balloons in the earlier stages of the Soudan campaign the affair would not have lasted as many months as it did years. This statement, however, should be read in conjunction with another of the same officer in the "Soldier's Pocket Book," that "in a windy country balloons are useless." In the Boer War the usefulness of the balloon was frequently tested, more particularly during the siege of Ladysmith, when it was deemed of great value in directing the fire of the British artillery, and again in Buller's advance, where the balloon is credited with having located a "death-trap" of the enemy at Spion Kop. Other all-important service was rendered at Magersfontein. The Service balloon principally used was made of goldbeaters' skin, containing about 10,000 cubic feet of hydrogen, which had been produced by the action of sulphuric acid on zinc, and compressed in steel cylinders. A special gas factory was, for the purpose of the campaign, established at Cape Town.