The supply and demand of emigrants were evidently entangled and it is unlikely that the propaganda machine was the first cause of the new scale and urgency of mass emigration. The years 1768 to 1776 may have marked an earlier fundamental discontinuity in emigration but the evidence is ambiguous. There is ample remaining contention among the migration scholars, and the views of the historical geographer Ian Whyte are typical of modern scepticism about the notion of any fundamental discontinuity in the long narrative of mobility. Strong support for the discontinuity thesis comes from the quantitative historians T.J. Hatton and J.G. Williamson. The American scholar Raymond Cohn has provided emphatic reinforcement to the claim of 'discontinuity' in the later 1820s when, he declares, that 'mass migration began'. He says there was a break in trend in Atlantic migration between 1827 and 1831.