NO CURVATURE ACROSS THE ENGLISH CHANNEL:
The original webpages as they appeared on flickr.com about four years ago:
The photographers are located right on the Cap Gris Nez beach, at an altitude of about 2-3 meters...the small rectangle in the photo is Cap Blanc Nez:
SHIPSPOTTING ON CAP GRIZ NEZ, ZERO CURVATURE ALL THE WAY TO ENGLAND, WHITE CLIFFS, DOVER:
No curvature whatsoever, a completely flat surface of the English Channel
white cliffs dover
Another photograph taken from Cap Gris Nez:
http://www.expedition360.com/journal/archives/2007/09/To meet the requirements of the RE, here are the numbers for different altitudes (we will go all the way to 20 meters, that is, the height of a five-story building):
h = 3 m BD = 60.6
h = 5 m BD = 53
h = 10m BD = 40.4
h = 20m BD = 25.5
That is, from an altitude of 20 meters, we would not see anything below 25.5 from the other side; the White Cliffs are in full view...
Let us go to Lake Michigan...
From Holland Michigan, across the Lake Michigan, lights of three different communities were seen (one of them Milwaukee), across a distance of 128 km.
http://nl.newsbank.com/nl-search/we/Archives?p_action=keyword&s_search_type=keyword&p_product=HSHH&p_theme=gatehouse (on the archive webpage, May 28, 2003, Oh Say Can You See article)
'As twilight deepened, there were more and more lights.'
Bringing out a pair of binoculars, Kanis said he was able to make out the shape of some buildings.
'With the binoculars we could make out three different communities,' Kanis said.
According to one Coast Guard crewman, it is possible to see city lights across the lake at very specific times.
Currently a Coast Guard crewman stationed in Holland, Todd Reed has worked on the east side of Lake Michigan for 30 years and said he's been able to see lights across the lake at least a dozen times.
THE CURVATURE FOR 128 KM IS 321 METERS.
THE HOUSE OF THOSE RESIDENTS IS LOCATED RIGHT NEXT TO THE LAKE, BUT LET US INVESTIGATE VARIOUS ALTITUDES, FOR THE SAKE OF DISCUSSION.
h = 3 meters BD = 1163 METERS
h = 5 meters BD = 1129 METERS
h = 10 meters BD = 1068 METERS
h = 20 meters BD = 984 METERS
h = 50 meters BD = 827.6 METERS
h = 100 meters BD = 667.6 METERS
The highest building in Milwaukee has a height of 183 meters, the difference from h = 5 meters in altitude being 946 meters, and those residents saw the buildings from THREE DIFFERENT COMMUNITIES, two of which have buildings whose heights measure way under 183 meters.
Therefore, the only way those buildings could be seen, given the 128 km distance, would be if the surface of Lake Michigan is completely flat (you can also use the above formula on atmospheric refraction to see how impossible it is to see shapes of buildings over a 128 km distance).
THE TALLEST BUILDING IN RACINE IS THE COUNTY COURTHOUSE, 40 METERS; IT WOULD BE ABSOLUTELY IMPOSSIBLE TO SEE THIS COURTHOUSE FROM 128 KM DISTANCE, FROM HOLLAND.