296 THE POPULAR SCIENCE MONTHLY. 



RECENT PROGRESS IN AERIAL NAVIGATION. 



Br Pbofessor W. LE CONTE STEVENS. 



BALLOONING has thus far been a French art : introduced a little 

 over a century ago by a Frenchman, Montgolfier ; rapidly de- 

 veloped by another Frenchman, Charles ; more practiced in France 

 than anywhere else in the world ; and recently improved by French- 

 men to such an extent that it is quite possible now on any fair day to 

 go an hour's journey through the air in any desired direction, even 

 against the wind. 



The history of the application of science to art has revealed a 

 number of cases in which practical success was secured by inventors 

 entertaining quite erroneous conceptions of the principles they were 

 applying. Somewhat vague stories are transmitted in regard to Roger 

 Bacon's suggestion, during the thirteenth century, of employing a 

 thin hollow globe of copper, " to be filled with ethereal air or liquid 

 fire and then launched forth from some elevated point into the atmos- 

 phere, where it will float like a vessel on water." Bacon gave no recipe 

 for making " liquid fire," nor did he calculate the dimensions of a 

 globe of copper to be filled with it that would have sufficient ascen- 

 sive power to lift a human being. He assures us " there is certainly a 

 flying instrument, not that I ever knew a man that had it, but I am 

 particularly acquainted with the ingenious person who contrived it." 

 His conception was never reduced to practice. It was merely a fair 

 specimen of current science in his time. He believed that the aerial 

 ocean around our earth had a definite boundary like the liquid ocean, 

 and that a body of sufficient lightness, if it could only be found, would 

 easily rise to this surface as a cork rises to the surface of water. 



More than three centuries after the time of Bacon, Father Lana 

 wrote out his idea of a vessel that might be made to rise in the air. 

 Four hollow globes of copper, each having a diameter of about twenty- 

 five feet, were to be carefully exhausted and then attached to a car. 

 Torricelli and Pascal had already proved that the pressure of the 

 atmosphere was nearly fifteen pounds per square inch at sea-level, and 

 Lana's proposed method of exhausting his globes was to be an appli- 

 cation of Torricelli's principle. Each globe was to be filled with water 

 and lifted to a height of at least thirty-four feet. Beneath it should be 

 fitted a tube with air-tight connections, which was to dip into water. 

 On opening this tube the contents of the globe would be emptied into 

 the vessel below, leaving a Torricellian vacuum above, while the tube 

 would become a water-barometer. Lana seemed to know nothing 

 about the specific gravity of gases. His copper globes were to be 

 made very thin in order to secure lightness, but he failed to make any 

 correct estimate of the rigidity they must have to sustain either the 



