Gas laws 1662 Robert Boyle studied the relationship between volume and pressure of a gas of fixed amount at constant temperature. He observed that volume of a given mass of a gas is inversely proportional to its pressure at a constant temperature. Boyle's law, published in 1662, states that, at constant temperature, the product of the pressure and volume of a given mass of an ideal gas in a closed system is always constant. It can be verified experimentally using a pressure gauge and a variable volume container. It can also be derived from the kinetic theory of gases: if a container,
Theory of intervening opportunities Theory of intervening opportunities Theory of intervening opportunities attempts to describe the likelihood of migration. Its hypothesis is that this likelihood is influenced most by the opportunities to settle at the destination, less by distance or population pressure at the starting point. Stouffer's law of intervening opportunities states, ""The number of persons going a given distance is directly proportional to the number of opportunities at that distance and inversely proportional to the number of intervening opportunities."" Stouffer theorises that the amount of migration over a given distance is directly proportional to the number of opportunities at the place of destination,