Scientific Discovery :
       Salt Brownrigg studied medicine at the University of Leyden before setting up practice in the Lake District.
He became interested in gas-related problems in the mines, and arranged to have flammable substances pumped directly into his house for experiments. However, the work that first brought him to national attention was his treatise on salt. Salt was widely used as a preservative for meat and fish but supplies were often unpredictable and hard to secure. On the continent, salt was made by using sun and wind to evaporate seawater. In England, the relative lack of sunshine meant that salt was usually made by heating brine (seawater) artificially. This process was expensive, as it required a great deal of fuel to manufacture sufficient quantities, and the resulting salt contained many impurities, including "seeds, sperm and excrements of innumerable kinds of plants and animals". Salt-makers also traditionally added material that would enable the salt to crystallise more rapidly; dog fat was particularly popular. However, Brownrigg argued that England did have enough sun to evaporate seawater into the finest salt, and conducted experiments in Hampshire to prove his case. His paper was published in the Philosophical Transactions of the Royal Society and he was elected a Fellow shortly afterwards.
       His fame secured, many eminent scientists traveled to see him in Cumbria. On one occasion he investigated the effect oil had on water, accompanied by the president of the Royal Society and the American scientist and diplomat Benjamin Franklin. Franklin had noticed that the wake of one ship he saw was particularly smooth, and was told that the cooks had probably just discharged greasy water through the scuppers. He discovered that Bermudans used oil to calm the water above fish they were going to spear and that Lisbon fishermen supposedly used oil to suppress the breakers as they returned to harbour.
      His curiosity aroused, Franklin determined to try this himself, and first did so on Clapham Common in London. In 1772 he and Sir John Pringle, President of the Royal Society, visited Brownrigg to pour oil onto Derwentwater. Franklin noticed how even a little oil spread dramatically, forming a film so thin that it produced what he called 'prismatic colours'; we now know that some oil films are just one molecule thick. Franklin speculated that the oil prevented the wind from 'getting a grip' on the water, not only preventing tiny ripples, but also stopping the wind from making existing waves bigger. In truth, the effect was probably more a result of surface tension trying to keep the oil film flat.