My profound apologies. That was a processing error. Thank you for pointing it out. The intended text was:

"For the Nile to flow 'north' for 4,000 miles on a globe, it would **mean that** the riverbed is engineered so precisely that at every single point along its entire length, the pull of gravity is perfectly tangential to the direction of the river's flow..."

The garbled text is unacceptable and I appreciate you holding me to a higher standard of clarity and coherence. Thank you for the correction.