-EARLY EXPERIMENTS IN AIR FLIGHT. bQ<^ 



liquid, wherever it happens to have been placed. This state of 

 indifferent equilibrium is, however, possible only if the weight of 

 the body remains rigorously constant. The slightest augmentation 

 of the weight immediately causes the body to descend, while the 

 slightest diminution sends it up. From this source arise the diffi- 

 culties that are met in the construction of submarine boats, when 

 their ascent or descent is obtained by means of air chambers, which 

 are filled with water or emptied of it according to the requirements. 

 The equilibrium of these engines is always precarious, and this ex- 

 plains why none of them, from that of Van Drebbel in 1620 to the 

 experiments of Goubet in 1895, have given really practical results 

 in the matter of stability of immersion. 



When Galileo, following Aristotle, had demonstrated the pon- 

 derability of the air, and Torricelli had proved that atmospheric 

 pressure was a result of that property, it was immediately thought 

 that the principle discovered by Archimedes might be extended 

 to the air, and Otto von Guericke gave an experimental demon- 

 stration of it by the invention of the baroscope. 



From this period it seems, then, that the discovery of aeronautics 

 was possible. If the weight of the volume of air displaced is 

 greater than that of the body, the latter should take an ascensional 

 movement in the atmosphere, as a cork does when plunged into 

 water; and it is evident that for a body to satisfy such conditions 

 we have only to fill a very light envelope with a gas less dense 

 than the ambient air. But the study of gases was still in its in- 

 fancy in the seventeenth century, and it required the labors of 

 Mortrel d'Element and Hales, at the beginning of the following 

 century, to teach physicists how to collect and retain them. 



The history of the progress of the human mind shows, further, 

 that the pure and simple acceptance of a scientific discovery is not 

 enough to make it produce all the consequences we have a right 

 to expect from it. It must, further, impregnating the mind with 

 itself, pass, v/e might say, into the condition of an innate idea. 

 Chemistry, in this very matter of the discovery of the weight of 

 the air and of the gases, presents a striking example of the accu- 

 racy of our proposition. The ponderability of the air had been 

 accepted by physicists for a long time, while chemists continued 

 to take no account of it, although, as Mendeleef has remarked, 

 no exact idea could be conceived, under such conditions, concerning 

 most chemical phenomena. It is to the glory of Lavoisier that 

 he first took account of this ponderability and of that of all the 

 gases as well. When we reflect that it was not till about 1775, or 

 a hundred and fifty years after Galileo, that this illustrious French- 

 man began to set forth those ideas, it is not any wonder that the 



