I realise that others on this list may not accept that this is a 
statement of the accelerator and think of Aftalion, Clark and 
Bickerdicke as the original formulators of the idea, but consider the 
following quotation from Hobson and Mummery (1889, pp. 85-6):

"Thus if a community increases its consumption from 10x wealth to 11x 
wealth a year, production must during the year in which this increase 
takes place exceed consumption by 4x wealth in order to accumulate 
the additional forms of capital required: that is to say, production 
must during this year amount to 15x wealth. So soon, however, as 
consumption, having reached 11x annually, no longer increases, a 
production of 11x annually alone is required."

As one might expect in a theorist who focused on the problem 
under-consumption, and the level of saving required to sustain a 
given growth rate, consumption is what drives the accumulation of 
capital. This would seem to echo the views expressed 20 to 30 years 
later that Daniele Besomi cites.

Roger Backhouse