By the same authority, at page 39, the Bidston Hill Lighthouse, near Liverpool, is 228 feet above high water, one bright fixed light, visible 23 nautical or very nearly 27 statute miles. Deducting 4 miles for the height of the observer, squaring the remaining 23 miles and multiplying that product by 8 inches we have a downward curvature of 352 feet; from this deduct the altitude of the light, 228 feet, and there remains 124 feet as the distance which the light should be below the horizon!
Again, at page 40:—“The lower light on the ‘Calf of Man’ is 282 feet above high water, and is visible 23 nautical miles.” The usual calculation will show that it ought to be 70 feet below the horizon!
At page 41 the Cromer light is described as having an altitude of 274 feet above high water, and is visible 23 nautical miles, whereas it ought to be at that distance 78 feet below the horizon!
At page 9 it is said:—“The coal fire (which was once used) on the Spurn Point Lighthouse, at the mouth of the Humber, which was constructed on a good principle for burning, has been seen 30 miles off.” If the miles here given are nautical measure they would be equal to 35 statute miles. Deducting 4 miles as the usual amount for the distance of the horizon, there will remain 31 miles, which squared and multiplied by 8 inches will give 640 feet as the declination of the water from the horizon to the base of the Lighthouse, the altitude of which is given at page 42 as 93 feet above high water. This amount deducted from the above 640 feet will leave 547 feet as the distance which the Spurn Light ought to have been below the horizon!
The two High Whitby Lights are 240 feet above high water (see page 42), and are visible 23 nautical miles at sea. The proper calculation will be 102 feet below the horizon!
At page 43, it is said that the Lower Farne Island Light is visible for 12 nautical or 14 statute miles, and the height above high water is 45 feet. The usual calculation will show that this light ought to be 67 feet below the horizon!
The Hekkengen Light, on the west coast of Norway (see page 54), is 66 feet above high water, and visible 16 statute miles. It ought to be sunk beneath the horizon 30 feet!
The Trondhjem Light (see p. 55), on the Ringholm Rock, west coast of Norway, is 51 feet high, and is visible 16 statute miles; but ought to be 45 feet below the horizon!
The Rondö Light, also on the west coast of Norway (see p. 55), is 161 feet high, and is visible for 25 statute miles; the proper calculation will prove that it ought to be above 130 feet below the horizon!
The Egerö Light, on west point of Island, south coast of Norway (see p. 56), and which is fitted up with the first order of the dioptric lights, is visible for 28 statute miles, and the altitude above high water is 154 feet; making the usual calculation we find this light ought to be depressed, or sunk, below the horizon 230 feet!