CHAPTER XXIII. 

 AERONAUTICS. 



PRESSURE OF AIR IN BODIES EARLY ATTEMPTS TO FLY IN THE AIR 



DISCOVERY OF HYDROGEN THE MONTGOLFIER BALLOONS FIRST 



EXPERIMENTS IN PARIS NOTED ASCENTS. 



IN the first part of this volume we entered into the circumstances of air 

 pressure, and in the Chemistry section we shall be told about the atmosphere 

 and its constituents. We know that the air around us is composed princi- 

 pally of two gases, oxygen and nitrogen, with aqueous vapour and some 

 carbonic acid. An enormous quantity of carbonic acid is produced every 

 day, and were it not for the action of vegetation the amount produced 

 would speedily set all animal life at rest. But our friends, the plants, decom- 

 pose the carbonic acid by assimilating the carbon and setting free the 

 oxygen which animals consume. Thus our atmosphere keeps its balance, so 

 to speak. Nothing is lost in nature. 



We have illustrated the pressure of the atmosphere by the Magdeburg 

 hemispheres, and we know that the higher we ascend the pressure is 

 lessened. The weight of the atmosphere is 15 Ibs. to the square inch at 

 sea level. This we have seen in the barometer. Now pressure is equal. 

 Any body immersed in a liquid suffers pressure, and we remember 

 Archimedes and the crown. It displaced a certain amount of water when 

 immersed. A body in air displaces it just the same. Therefore when any 

 body is heavier than the air, it will fall just as a stone will fall in water. 

 If it be of equal weight, it will remain balanced in the air, if lighter it will 

 rise, till "it attains a height where the weight of the atmosphere and its own 

 are equal ; there it will remain till the conditions are altered. Now we will 

 readily understand why balloons float in the air, and why clouds ascend and 

 descend in the atmosphere. 



In the following pages we propose to consider the question of balloon- 

 ing, and the possibility of flying. We all have been anxious concerning the 

 unfortunate balloonist who was lost in the Channel, so some details concern- 

 ing the science generally, with the experiences of skilled aeronauts, will guide 

 us in our selection of material. We will first give a history of the efforts 

 made by the ancients to fly, and this ambition to soar above the earth has 

 not yet died out. 



