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. It is here that reference must be made to some of the special work undertaken by Mr. Eric S. Bruce, which dealt with the management of captive balloons under different conditions, and with a system of signalling thus rendered feasible. Mr. Bruce, who, since Major Baden-Powell's retirement from the office, has devoted his best energies as secretary to the advancement of the British Aeronautical Society, was the inventor of the system of electric balloon signalling which he supplied to the British Government, as well as to the Belgian and Italian Governments. This system requires but a very small balloon, made of three or four thicknesses of goldbeaters' skin, measuring from 7 to 10 feet in diameter, and needing only two or three gas cylinders for inflation. Within the balloon, which is sufficiently translucent, are placed several incandescent lamps in metallic circuit, with a source of electricity on the ground. This source of electricity may consist of batteries of moderate size or a portable hand dynamo. In the circuit is placed an apparatus for making and breaking contact rapidly, and by varying the duration of the flashes in the balloon telegraphic messages may be easily transmitted. To overcome the difficulty of unsteadiness, under circumstances of rough weather, in the captive balloon which carried the glow lamps, Mr. Bruce experimented with guy ropes, and gave a most successful exhibition of their efficiency before military experts at Stamford Bridge grounds, though a stiff wind was blowing at the time.