There is a good deal of difference of opinion as to the altitude which the Zeppelin can attain. When fully loaded in war trim the latest ships can rise to about 5,000 feet, but by the time they reach London, for example, and have used nearly half their fuel, ammunition, &c., they are several thousand feet higher. The practical limit to airship work is said to be about 10,000 feet. Above that height the cold is so intense, the air so rarefied, and the conditions for men, engine, and ship so distressing, that there is no inducement to rise further. It is noteworthy that the latest type of Zeppelin is fitted with a switchboard for dropping bombs, as, for example, in the airship brought down in the north of London in the early part of October, 1916. The German Schütte-Lanz, a well-known type, is an attempt to secure the advantages of a rigid type, without the fragilities of the Zeppelin. The framework is made of fir wood, and contains separate gas compartments. Exceptional strength is claimed for these compartments. A centrifugal pump is employed for distributing the gas. The volume of the airship is 918,000 cubic feet—an extremely large structure, surpassing even some of the largest types of airship. It is believed in authoritative quarters that one of the first airships brought down in flames on British soil was a ship of this type. The German Gross airship has been described as more or less a reproduction of the Lebauchy type, which is, of course, of French origin. It is built partially on the rigid and partly on the non-rigid system. The Parseval airship is portable, and therefore a particularly useful type. On account of its subtleness it has been remarkably free from accidents. It is small in size, and is fitted for many purposes for which larger airships would be useless. The dimensions, however, of the Parseval vary considerably, the smallest being 3,200 cubic metres. (This particular ship was built in the year 1908.) The more recent and larger designs have a far greater capacity. There are, of course, many other types on similar lines, but we are chiefly concerned in these pages with the purpose and fate of airships of the rigid type, and in our next chapter we shall see how our airmen have fitted themselves for the task of dealing with Zeppelins. CHAPTER VIII CONTROLLING AN AEROPLANE It need scarcely be said that the control of an aeroplane very greatly depends upon the pilot. One pilot will perform marvels with a machine which in the hands of another may produce a very different result. There are, of course, rules which must be observed. But to the skilful pilot an aeroplane may be said to be like a horse under the care of a trained horseman. A light touch will achieve more than the most strenuous efforts of the amateur, and out of the seemingly wayward machine the expert aviator will make a docile and obedient servant.