14. “The Lieutenant-Colonel Portlock experiment used oxy-hydrogen Drummond’s lights and heliostats to reflect the sun’s rays across stations set up across 108 miles of St. George’s Channel. If the Earth were actually a ball 25,000 miles in circumference, Portlock’s light should have remained hidden under a mile and a half of curvature.” 

The source is the same, the alleged “Doctor” Rowbotham of very dubious qualifications and medical understanding.  See Garwood, Christine (2010). Flat Earth: The History of an Infamous Idea Pan Macmillan.

And again, the numbers are wrong. 

It’s quite possible to see that mountain in Ireland from the Welsh Preselli Hills. The height needed is 1,437 feet, and the highest peak in Preseli is 1,759 feet. No problem.

http://the-uncredibles.tumblr.com/post/130629473404/200-pensb-14-lt-col-portlock

As Daimonie puts it,  “Another way of saying Dubay don't understand what the horizon is. See approximately all previous points” .