See Mirrlees for the history
1840 P. and W. McOnie was established by the 3 McOnie brothers to manufacture sugar machinery in Glasgow.
By 1848 the McOnie's concern had manufactured fifty engines and fifty mills. In that year the partnership was dissolved, William and Andrew McOnie formed W. and A. McOnie
1848 Peter McOnie joined with James Buchanan Mirrlees, forming McOnie and Mirrlees.