This arrangement allows the water displaced by the passage of a narrow boat to flow easily under the towpath and around the boat, enabling relatively free passage.
It is written with the author's usual readable flow, with a style that somehow suggests (without being overt and therefore off-putting) an acquaintanceship between author and reader.
The activity of ions at the electrode surface changes when there is current flow, and there are additional overpotential and resistive loss terms which contribute to the measured potential.
