Traditionally, there was not one dialect in Yorkshire but several. The Yorkshire Dialect Society draws a border roughly at the River Wharfe between two main zones. The area to the southwest of the river is more influenced by Mercian dialect whilst that to the northeast is more influenced by Northumbrian dialect. The distinction was first made by A. J. Ellis in "On Early English Pronunciation". The division was approved of by Joseph Wright, the founder of the Yorkshire Dialect Society and the author of the "English Dialect Dictionary". Investigations at village level by the dialect analysts Stead (1906), Sheard (1945) and Rohrer (1950) mapped a border between the two areas. A rough border between the two areas was mapped by the Swiss linguist Fritz Rohrer, having undertaken village-based research in areas indicated by previous statements by Richard Stead and J.A. Sheard, although there were "buffer areas" in which a mixed dialect was used, such as a large area between Leeds and Ripon, and also at Whitgift, near Goole.