In Reply to: Set the Thames on fire posted by Ray Lowrey on March 12, 2009 at 12:39:
: Referring to the request for the derivation of : "He'll never set the Thames on fire" ... my understanding has always been that this refers to the sieve which was manually operated at the end of the process when grinding grain. If the operator was keen enough, they would sift so fast that the 'thames' (what the sieve was called, apparently)would get warmed by the friction. Whether it could be operated fast enough to burst into flames is a matter for conjecture, but obviously the slower it was operated, the cooler it remained and the less dilligent was the operator.
There was a Middle English word "temse" meaning a sieve for sifting ground meal, but it certainly has nothing whatever to do with the phrase. There is an equivalent French phrase about "setting the Seine on fire", and a German phrase "das Rhein anzuenden" (set the Rhine on fire) which dates back at least to 1630. All these sayings are probably modelled on a classical Roman proverb, "Tiberium accendere nequaquam potest" - "he'll never set the Tiber on fire"; the meaning of which is obvious. (VSD)