This Day in History: 1855-07-07

Michael Faraday’s letter on pollution is written this day in 1855 and published in the Times of London. The letter detailed the state of pollution of the Thames River and the use of his business card to measure water opacity. His observations became famous, in part because of a Punch magazine cartoon, in which Faraday is humorously seen “giving” his card to Father Thames while holding his nose from the stench.

Faraday said in his 1855 letter:

“The whole of the river was an opaque pale brown fluid. In order to test the degree of opacity, I tore up some white cards into pieces, moistened them so as to make them sink easily below the surface, and then dropped some of these pieces into the water at every pier the boat came to; before they had sunk an inch below the surface they were indistinguishable, though the sun shone brightly at the time; and when the pieces fell edgeways the lower part was hidden from sight before the upper part was under water… If there be sufficient authority to remove a putrescent pond from the neighbourhood of a few simple dwellings, surely the river which flows for so many miles through London ought not to be allowed to become a fermenting sewer… If we neglect this subject, we cannot expect to do so with impunity; nor ought we to be surprised if, ere many years are over, a hot season give us sad proof of the folly of our carelessness.”

The technique of measuring opacity using a card is still in use, with refinements, as the Secchi test for water transparency. It was developed in 1865 by Father Angelo Secchi.
Additional resources: Cholera and the Thames; and Thames River pollution.