THE WOMBAT. 6l 



is made of a triple thickness of silk, for the lower part a double 

 thickness being deemed sufficient, and this silk is thickly covered 

 with two layers of varnish, both inside and outside It is thus 

 almost impermeable Experiments have shown that the waste of 

 gas in a balloon of 8 metres diameter causes a loss in one month of 

 six kilogrammes of its carrying power, and this balloon of 23 metres 

 will lose 50 kilograms in 30 days, i.e., B V of its total carrying power 



There is another condition besides the construction of the 

 balloon which will operate favourably, and that is the extremely 

 slow diffusion of the gas — according to experiments at Spitzbergen, 

 and the remarkably even conditions of temperature and pressure in 

 the polar regions, and there will be little or no likelihood of the ice 

 layers being formed thickly on the outside of the balloon, and thus 

 effecting its carrying power. Andree's balloon is not intended to 

 rise more than from fifty to two hundred metres above the surface, 

 and the originality of its construction lies in the employment of 

 dragging or guide ropes which work in connection with three sails 

 fixed to the balloon. The guide ropes, however, are movable, and 

 by putting friction on one side or the other, they can make the 

 balloon turn on a vertical axis, and so present any required angle of 

 the sails to the wind. The guide ropes could act so as to keep the 

 balloon moving at a different angle from the wind, and to regulate 

 the altitude. The higher the balloon ascends the greater becomes 

 the weight of rope, while if it descends the weight of rope becomes 

 smaller. Andree, assisted by Strindberg, tried this experiment several 

 times, and always with success. These ropes are about 1,000 yards 

 long, in lengths of 100 yards. 



The balloon floats at a height of about 250 metres above the 

 surface, i.e., below the lowest clouds, but above the fogs. The 

 dragging of the cables will cause no danger, as in the polar regions 

 the surface is comparatively smooth and free from vegetation. The 

 guide ropes are saturated in vaseline for 100 feet, so that they may 

 float if immersed in water : — the vaseline will also diminish friction. 



The explorers carried a " navis-azimuth," an apparatus of 

 English invention, which serves at the same time as an altazimuth 

 and an equatorial. It is comparatively easy by the aid of this 

 instrument to determine the longitude and latitude near the pole, 

 simply by observations of the moon or sun taken at Greenwich 

 time by the chronometer. The instrument can also serve as a 

 sextant, and is most useful in ascertaining the speed of the balloon. 

 The car is composed of two parts : — a lower chamber 5 ft. high 

 and 6£ ft in diameter, which is entered by a trap door, so that the 

 passenger can creep in and sleep comfortably ; the observatory 

 above, about 8 ft in diameter, and surrounded by a railing on 

 which all the instruments are fixed ; there are collected all in- 

 struments which science could lend, to aid in observations in 

 astronomy, geography, and meteorology, many of these instruments 



