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 Friedmann-Lemaître-Robertson-Walker metric: by dividing the equation above with formula_10 and identifying formula_11 (the energy density), we get one of the FLRW equations of motions. In the comoving coordinates, formula_12 is equal to the mass density formula_13. For radiation, formula_14 whereas for matter formula_15 thus formula_12 is proportional to formula_17 For matter formula_18 thus formula_12 is proportional to formula_20 This can be understood as follows: For matter, the energy density is equal (in our approximation) to the rest mass density. This is inversely proportional to the volume, and is therefore proportional to formula_20. For radiation, the energy density depends on