1776-1844. British chemist, the first in 
modern times to propose the existence of 
atoms, which he considered to be the 
smallest parts of matter. He produced the 
first list of relative atomic masses, 
Absorption of Gases 1805. He was also the 
first scientist to note and record 
colour-blindness. From experiments with 
gases he noted that the proportions of two 
components combining to form another gas
were always constant. From this he suggested
that if substances combine in simple
numerical ratios then the macroscopic weight
proportions represent the relative atomic
masses of those substances.