Jacques Charles was a French inventor and scientist. He published the law saying that volume and temperature are directly proportional. Charles's law was first published by Joseph Gay-Lussac, but Gay-Lussac gave credit to Charles in his works. Even before this, John Dalton had discovered this law. He was not thorough about it, so Gay-Lussac and Charles went more in-depth. This is easy to explain with bike tires. On a hot day, you inflate your bike tires to the right psi. They seem to be perfect. On a cold day when you choose to ride bike, you see that the tires are low, and more air must be added. This is Charles's Law at work.