John Dalton contributed to the development of the modern atomic theory. He also contributed to findings in the field of colorblindness. Specifically, in 1803 Dalton published the Law of Partial Pressures. The Law of Partial Pressures states “ that in a mixture of non-reacting gases, the total gas pressure is equal to the sum of the partial pressures of the individual gases”. As well, in 1803 proposed his own “atomic theory” using round atoms, and it was based upon measurable properties of mass.