This table is for

statute miles.

Does that mean it applies only for lighthouses when viewed over land?

And for a 15 foot tall observer. Hmmm.

Maybe Ross standing on the cab of a pickup with Hersh standing on his head and Hersh observing,

and Leah driving the truck.

To be serious, the observer columm was based on an assumed eye level 15 feet above sea level when standing on a sailing vessel deck. To use this table accurately one must know approximately how high their eye level is above sea level and add the appropriate number obtained from the distance in miles column.

Example:

Lighthouse 75 feet and eye level 25 feet. The distance for the lighthouse is 11.7 miles. Add to this for the observer from this table a distance of 6.6 miles for 25 ft of height. Therefore the distance of visibility from the observer to the lighthouse is 11.7 + 6.6 = 18.3 miles.

If the eye of the observer is at 50 feet then add 9.4 miles to the 11.7 miles for the lighthouse. The distance seen now becomes 21.1 miles. It would be 25 miles if observed from 100 ft elevation.

So how many miles can a lighthouse be seen? Depends on where you are standing as much or more so than the height of the lighthouse.