Jaggers gained his practical experience of mechanics, working in Yorkshire's cotton manufacturing industry. He extended his experience to the behaviour of a roulette wheel, speculating that its outcomes were not purely random numbers but that mechanical imbalances might result in biases towards particular outcomes.
In 1873, Jaggers hired six clerks clandestinely to record the outcomes of the six roulette wheels at the Beaux-Arts Casino at Monte Carlo, Monaco. He discovered that one of the wheels showed a clear bias, in that nine of the numbers occured more frequently than the others. Exploiting this characteristic, Jagger made a profit of USD 450,000 before the casino mangement intervened to modify the wheels.
A popular song The Man Who Broke the Bank at Monte Carlo was written about his exploits in 1891 by Fred Gilbert.