Peter Alexeivitch Kropotkin and John Thomas Bealby, 1911 Encyclopædia Britannica, Volume 8… (1911)
“ Except at the rapids the current of the Dvina is comparatively slow, as the average fall per mile is only 9 in. Till its union with the Vychegda, a river which exceeds it in volume, it flows for the most part in a single, well-defined and permanent channel ”
