342 AERONAUTICS 



consisting of a rigid indeformable framework, possesses a considerable degree of strength, 

 moreover, the cars containing the engines, the propellers and the controlling organs, can 

 be rigidly attached to the hull and in close proximity thereto; so that the rigid dirigible 

 realises most nearly that ideal condition wherein the centres of resistance and propulsion 

 coincide. On the other hand, the rigid framework implies a great increase in weight; 

 hence a rigid dirigible must necessarily be of large size. Again, it can only be deflated 

 slowly, so that in case of accident or involuntary landing, it always stands in danger of 

 destruction by the wind. Lastly, being incapable of being transported, it can only act 

 from a fixed base. The non-rigid type, on the other hand, while it can be easily deflated 

 and transported, is of inferior structural strength and efficiency, for its gas-containing 

 hull is constituted by fabric the shape being maintained by keeping the gas under a 

 pressure in excess of that of the surrounding atmosphere while the propelling plant 

 and controlling surfaces must be situated in or near the car. 



The rigid dirigible, which owes its development chiefly to Count von Zeppelin, has 

 realised the more important progress. The last Zeppelin dirigible built before the end 

 of 1912, and acquired by the German navy, possessed a volume of 776,000 cubic feet 

 divided into 18 gas compartments; its length was 525 feet, its diameter 49 feet; driven 

 by three motors developing 510 total horse-power, it was capable of a speed of 52 miles 

 an hour, and carried a useful load of approximately 7 tons, sufficient to provide fuel for 

 96 hours. The framework of the Zeppelins is constituted by aluminium girder work. 

 In the Schiitte-Lanz dirigible, and in the recent French dirigible built to the designs of 

 M. Spiess, the skeleton is built up of wood. As passenger craft, the two Zeppelin dirigi- 

 bles owned by a private German company, rendered an excellent account of themselves 

 during the year 1912, making over 300 ascents and carrying about 5,000 passengers. 



Both the French and German armies possess a considerable fleet of dirigibles, the 

 numbers of efficient vessels being, at the end of 1912: 



Rigid. Semi-Rigid. Non-Rigid. Total. 

 Germany .... , . . . '. 5 3 5 13 



France . . . . '. . . : . ' . ' . r 3 8 12 



In addition both countries possess several privately-owned airships, available for 

 emergency service, which bring the German and French fleets up to 25 and 21 units 

 respectively. Further, both countries possess a large number of permanent airship 

 stations, situated principally in strategical centres. During manoeuvres of recent 

 years, and during the Tripolitan war in 1911-12, military dirigibles took part with 

 good results and demonstrated their special adaptability for night-work, for detailed 

 observation over long distances, and for maintaining uninterrupted communication 

 with their base by means of wireless telegraphy. In Great Britain progress has been 

 comparatively slow. Three small dirigibles built at the Royal Aircraft Factory for 

 experimental purposes have only proved partially successful, while the rigid dirigible 

 constructed for the Navy at Barrow was wrecked by the wind in 1911 on its first ap- 

 pearance in the open. These failures were followed by the British Government order- 

 ing, for the use of the Navy, a German dirigible of the Parseval system and a French 

 dirigible of the Astra-Torres type, towards the end of 1912. 



The wonderful progress in aviation during the last two years, and its transition from 

 the experimental to the practical stage has been clue principally to the improved aerody- 

 namical knowledge resulting from scientific research work previously allud- 

 iea ' ed, to and, though in lesser degree, to the increased skill and experience of 

 aeroplane pilots. In essential principles no radical alteration has taken place since the 

 days of Wilbur and Orville Wright, and the early French experimenters. By the side of 

 improvements in details of design, highly improved methods of construction have con- 

 tributed to increase the efficiency, reliability and safety of the aeroplane to a vast extent. 



Most noteworthy of modern technical features in aviation are the gradual introduc- 

 tion of steel where wood was the constructional material a most exclusively used a few 

 years ago, the substitution of a long covered-in body, forming the back-bone of the 



