There has been no lack of attempts to reach the highest altitudes. Up to the present, mankind has been able to reach an altitude of 11,800 meters in an airplane, 12,000 meters in a free balloon, and 8,600 meters on Mount Everest (Figure 9).
Figure 9. With increasing altitude, the density of air decreases extremely rapidly, as can be seen from the curve drawn on the right and from the intensity of the shading.
Key: 1. Altitude in km; 2. Balloon probe 35 km; 3. Projectile of the German longrange cannon; 4. Airplane 8 km; 5. Free balloon 12 km; 6. Scale for the density of air at various altitudes; 7. Normal density of air above sea level
Socalled balloon probes have attained even higher altitudes. They are unmanned rubber balloons that are supposed to carry very lightweight recording devices as high as possible. Since the air pressure decreases continually with increasing altitude, the balloon expands more and more during the ascent until it finally bursts. The recording devices attached to a parachute gradually fall, recording automatically pressure, temperature and the humidity of the air. Balloon probes of this type have been able to reach an altitude up to approximately 35 kilometers. Moreover, the projectiles of the famous German longrange cannon, which fired on Paris, reached an altitude of approximately 40 kilometers. Nevertheless, what is all of this in comparison to the tremendous altitudes to which we would have to ascend in order to reach into empty outer space or even to distant celestial bodies!