So I went through the USCG New England section of the “Light List” I referenced earlier and randomly selected lighthouses I could find in Findlay’s book. Interesting results:

(Per Rowbotham, 16’ Observer height)

Findlay:

Cape Ann Light, Height: 98’ Range: 16 NM (18.4125 statute miles)

Geographic Range/Curve Calc: 23’ below horizon

US Coast Guard:

Cape Ann Light, Height: 166’ Range: 17 NM (19.5633 statute miles)

Geographic Range/Curve Calc: 23’ above horizon

Findlay:

Minots Ledge Light, Height: 84’ Range: 14 NM (16.1109 statute miles)

Geographic Range/Curve Calc: 0 above horizon, 0 below horizon

US Coast Guard:

Minots Ledge Light, Height: 85’ Range: 10 NM (11.5078 statute miles)

Geographic Range/Curve Calc: 56’ above horizon

Findlay:

Race Point Light, Height: 35’ Range: 11 NM (12.6586 statute miles)

Geographic Range/Curve Calc: 5’ below horizon

US Coast Guard:

Race Point Light, Height: 41’ Range: 14 NM (16.1109 statute miles)

Geographic Range/Curve Calc: 43’ below horizon

See if you can figure out what’s going on. I think the thrust here is that using just Rowbotham’s geographic calculation alone does not tell the whole story. It’s only one part of the equation. It’s a convenient argument, but it seems that’s all it is, convenient. It’s incomplete.