In the 1810's, Gay-Lussac and Avogadro made an amazing discovery: The mysterious constant is just the molecular weight of the gas, if the amount of gas is measured in the right units. A good choice for the right unit is the ''mole'', which is the mass, in grams, that matches the molecular weight of the gas. (By then atomic weights and molecular weights were beginning to be understood.) This led to the [[Ideal Gas Law|Universal Gas Law]] or Ideal Gas Law: | In the 1810's, Gay-Lussac and Avogadro made an amazing discovery: The mysterious constant is just the molecular weight of the gas, if the amount of gas is measured in the right units. A good choice for the right unit is the ''mole'', which is the mass, in grams, that matches the molecular weight of the gas. (By then atomic weights and molecular weights were beginning to be understood.) This led to the [[Ideal Gas Law|Universal Gas Law]] or Ideal Gas Law: |