The 39th and 40th George III., cap. 98. An Act to prevent testators from leaving their property to accumulate for more than twenty-one years. So called because it was passed in reference to the last will and testament of the late Mr. Thelusson, in which he desired his property to be invested till it had accumulated to some nineteen millions sterling.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894