John Snow (1849) is a physician for Queen Victoria and great epidemiologist. He is a philosophical genius because he could control cholera in London even before the causative organism was discovered and found out how cholera spreads. His genius showed in his meticulous and scientific way of conducting the natural experiment to prove his hypothesis that contaminated water is the vehicle for the cholera spread. He thoughtfully considered all other causes that may confound his hypothesis and wisely neutralized them. He had seen that no difference whatever existed, either in the houses or the people receiving water supply of two water companies, or in any physical conditions with which they are surrendered.