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
Thermodynamics of the universe the temperature formula_22 as well, and is therefore proportional to formula_23. As the universe expands it cools down, so formula_22 depends on formula_9 as well. In fact, since the energy of a relativistic particle is inversely proportional to its wavelength, which is proportional to formula_9, the energy density of the radiation must be proportional to formula_17. From this discussion it is also obvious that the temperature of radiation is inversely proportional to the scale factor formula_9. Plugging this information to the Friedmann-Lemaître-Robertson-Walker equations of motion and neglecting both the cosmological constant formula_29 and the curvature parameter formula_30, which is justified