set the Thames on fire

To achieve something amazing but to a nearly-impossible degree; to do something which brings great public acclaim.

The origin of the expression is not settled, though one popular theory rests upon the linguistic misconstrual of the word *temse*, a sieve used in sifting flour. The suggestion is that a labourer might work with such vigour as to set the wooden rim of the sieve on fire through the heat of friction. This transition from a domestic implement to a major waterway is generally regarded as a failure of the ear rather than a geographical observation.

Alternative explanations involve more dramatic, if less frequent, occurrences. It has been proposed as a reference to lightning strikes along the Thames, which have historically ignited trees or resulted in unusual deaths along the banks. Others view the phrase as simple hyperbole, drawing upon the inherent difficulty of igniting a body of water.

While the image evokes the Great London fire of 1666, there is no direct evidence linking the idiom to that particular administrative inconvenience. The river served as the fire’s primary boundary rather than its fuel; however, the improbability of the Thames itself burning has remained the operative sentiment since the phrase entered the lexicon.