Ringelmann scale. A evaluate of smoke colour. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is essentially a card with squares of black, white and shades of grey which is held up and also the comparative grayness with the smoke judged. This 1670 portray exhibits enslaved Africans https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/