KECENT AERONATTTICAL TKOGKESS. 125 



be })ropolk'<l — till' skill will \ ibratc iiiul add t(^ the resistance; the nose, 

 unless distended l)v framework, will l)e dri\en in and oiler o-roat 

 resistance: the lias will he driven haek toward the after end. and the 

 ]>alaiice l)e disturlx'd. To j)rescrve this necessary rigidity all the 

 earlier iiaviiiabic balloons were kei)t taut by means of the l)alloiiet, 

 but Count Zeppelin eliected this ])y an internal framework. 



Count Zc})pelin, as I haxc said, struck out a new line. l>v greatly 

 increasin*^" the size of the balloon, he had obtained so much more lift- 

 ing- power as to be able to add a complete fi^uuework that stitiened it. 

 But it was probably solely owiii*^' to this ureat size that the apjiaratus 

 faileci to be practically manageable. It may be compared to the (jreat 

 Kdiifcrit steamship, 1)ut with the diti'erence that at the time of its con- 

 struction we had l)ut the most elementary experience of air vessels 

 propelled by engines. At the same time this enormous ca])acity had 

 its advantages. Ibid it been of half the diameter and half th.e length, 

 though the resistance to pro})ulsioi! might have been only one-(piarter, 

 the \olume and the lifting })()wer would only have been one-eighth. 

 So that, instead of carrying engines of 82diorsepower, as was done, it 

 might have only lieen possible to carry some of -idioi'sepower. Dr. 

 Pole, in his most valual)le little treatises, years ago point(>d out the 

 advantages of very large volume. 



One result, then, of recent experiments is that it seems quite practi- 

 cable to build a navigable balloon to go, we will say, 15 miles an hour. 

 This, however, is not quite enough. As the wind so often blows faster 

 than this, it is unsafe to let the balloon out on any l)ut a very calm 

 day; else, though only blowing 16 miles an hour, the machine will 

 inevitably ))e carried oft' and have to descend in strange fields far from 

 its shed, and the ditliculties of transporting it back may be so great 

 that it may even have to be taken to ])ieces. Having successfully 

 accomplished this much, however, it certainly looks as if we could 

 improve a little titid get the balloon to travel 20 or 'Ih miles an hour, 

 which would be suliicient to stem the ordinary light lueezes. 



We have learned many practical lessons from these recent experiences. 

 It is necessary to make efficient provision against the balloon ca\ing in 

 or buckling up. It is, of course, most important that the engine shall 

 be so constructed as not by any possible means to lie able to ignite the 

 gas in the balloon. I)ut (\specially we have learned that — speaking in 

 general terms — for a cigar-shaped vessel some 20 feet in diameter it is 

 necessary to apply a power of more than 1(1 horsepower (presuming 

 no exceptionally efficient propeller l)e found) for it to be really etli- 

 cient. This practically means that you must lune a larger balloon. 



MM. Lebaudy have now adojited a larger balloon, enabling them to 

 carry an engine of -to horsepower, or more than double the power of 

 that of M. Santos Dumont. C-olonel Renard, also, is ahout to build 

 one larger still, of some '.»o,ooo cubic feet. Dr. Barton's proposed air 

 ship is also designed to be of great size. 



