Steam digester Torricelli and further developed by German scientist Otto von Guericke with his Magdeburg hemispheres. Guerike's demonstration was documented by Gaspar Schott, in a book that was read by Robert Boyle. Boyle and his assistant Robert Hooke improved Guericke's air pump design and built their own. From this, through various experiments, they formulated what is called Boyle's law, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Soon the ideal gas law was formulated. Based on these concepts in 1679 a Boyle's associate, named Denis Papin, built a "bone digester", which is
Lifting gas of the lifting capability of hydrogen to that of helium will remain the same. This calculation does not include the mass of the envelope need to hold the lifting gas. At higher altitudes, the air pressure is lower and therefore the pressure inside the balloon is also lower. This means that while the mass of lifting gas and mass of displaced air for a given lift are the same as at lower altitude, the volume of the balloon is much greater at higher altitudes. A balloon that is designed to lift to extreme heights (stratosphere), must be able to expand