The Polar Airship 



2 11 



the little holes made by the needle, all 

 the sewing lines are covered with bands 

 of fabric cemented to the envelope — 

 first a band covering the seam, and over 

 that still another and wider one. The 

 primary purpose of these interior bands 

 is to make the envelope as nearly as 

 possible gas-tight, but they also add 

 greatly to the tensile strength of the 

 skin. 



The outer surface of the balloon is 

 quite smooth. There is no netting of 

 cordage or of wires to hold moisture, 

 snow, or frost. Besides, the outer sur- 

 face is a coating of rubber, which will 

 serve to shed the rain and snow and 

 prevent moisture entering the fabric. 

 In effect the double reinforcing bands 

 which cover the seams, circumferen- 

 tially and longitudinally, act as an in- 

 terior netting, consolidated with the 

 envelope, and increasing materially its 

 powers of resistance to all stresses. 

 This added tensile strength is not com- 

 puted in the coefficient of 5 to 1. 



No means has as yet been found of 

 making, with fabrics, an absolutely gas- 

 tight reservoir. In varnished silk bal- 

 loons, even when of two or three thick- 

 nesses of material, the loss ranges from 

 i 1 /^ to 3 per cent daily. With fabrics 

 coated with caoutchouc these losses are 

 materially reduced ; and with our three- 

 fold material and three coatings of rub- 

 ber we shall, according to the experts, 

 approximate very closely to gas-tight- 

 ness. M. Godard's contract calls for 

 an envelope from which the loss by 

 leakage shall not exceed 1% per cent in 

 24 hours, and he is convinced the loss 

 will not be more than one-half of his 

 maximum allowance. A loss of even 

 2 per cent per day would not be great 

 enough to interfere with the plans of 

 the expedition. 



THE WEIGHT OF THE BALLOON 



The weights of the various materials 

 entering into the construction of the 

 huge balloon will be approximately as 

 follows : 



Pounds. 

 Fabric of the envelope, and rubber 



coatings 2,200 



Reinforcing bands 225 



Etraves and relingues (for suspension 



of car) 100 



Five valves no 



Balloonet of light varnished silk 225 



Total 2,860 



Allowing for the three thicknesses, 

 for the laps, and for wastage in cutting, 

 approximately 12,000 square yards of 

 fabric will be required. The. cost of 

 material is about $1.50 per yard as it 

 comes from the factory. 



It is the judgment of all the aero- 

 nautic engineers whom I consulted in 

 Paris that M. Godard is constructing 

 for our expedition the strongest and 

 most enduring gas envelope known to 

 the history of the art. 



SPEED 0E THE BIG AERONEE 



When we start in our airship from 

 Spitzbergen for the North Pole — and 

 we entertain hopes of being able to set 

 out in the latter part of next July or the 

 early part of August — we expect to be 

 able to advance at an average rate of 

 about 12 geographical miles per hour ; 

 that is to say, this is the mean speed 

 which has been assumed as the basis of 

 our calculations. At one hour it may 

 be greater, at another smaller; but this 

 is the expected average. Of course, in 

 speaking of the speed of a dirigible we 

 always have in mind what the French 

 call its "proper speed" — its speed of its 

 own force in calms, the speed it could 

 make wholly with its own means of 

 propulsion, irrespective of the helping 

 or the hindering of the winds. The ef- 

 fect of the wind upon the movement of 

 an airship, whether in France, in Amer- 

 ica, or the Arctic regions, is precisely 

 this : The velocity of the wind is to be 

 subtracted from or added to the proper 

 speed of the ship, according as whether 

 the wind is adverse or favorable on the 

 course one is sailing. For example, if 

 an airship is steering northward, with a 



